The year is 1973, and Col. Edward Carruthers, renowned for being the first man to ever be shot into space, has been discovered as the only survivor of a previous mission to Mars after his ship crashed on the planet. A rescue ship picks him up and blasts off from the planet to take him back to Earth... where he is to stand trial for the murder of his entire crew. Carruthers maintains that he didn't kill them, that the killer was actually some sort of violent, Martian creature. Col. Van Heusen, the commander of the rescue ship, isn't convinced, speculating that Carruthers murdered the members of his crew so he could use the ship's food and water rations to keep himself alive for as long as necessary, seeing as how he had no way of knowing when or even if a rescue ship would arrive. His discovery of a human skull with a bullet-hole in it has him completely convinced. Van Heusen decides to keep a guard on Carruthers at all times and intends to have his confession on tape by the time they reach Earth. However, inbound to Earth, two members of the crew, Joe Kienholz and Gino Finelli, disappear. During the search for them, the former's body is found stuffed in an air duct and the latter is found in another one, alive but barely. But, when Maj. John Purdue tries to save Gino, he's attacked and injured by the killer: a scaly, reptilian, humanoid creature that stowed away in the ship's cargo bay before it took off from Mars. The monster proves to be immune to bullets, gas, explosives, electrocution, and even exposure to the ship's nuclear reactor, forcing the crew to simply put up barriers between it and them on the various levels of the ship, which only work for so long, as it can tear through metal. An autopsy on Kienholz's body reveals that it absorbed every bit of edible fluid within his body and, what's more, the injures it inflicted upon Purdue and, at a later point, Van Heusen become infected with a Martian bacteria that is virtually impervious to normal drugs. Worst of all: the crew is running out of levels on the ship to use as shelter, meaning that by the time they reach Earth, there might not be anybody left alive.
As I said earlier, after Van Heusen is injured, Eric Royce (Dabs Greer) becomes the new leader of the crew along with Carruthers, although that's one of the few things about him that is memorable. He's one of the more underdeveloped characters, although he does have something of a personality in how he makes cracks about not giving up on a chess game with Carruthers and, when Kienholz disappears, he says, "If this is one of his jokes, I'll make him walk home!" He's also fairly intelligent, in that he comes up with a possible theory for the creature's origin, and helps in coming up with plans to deal with it, although they all end in failure. Like Carruthers, he realizes near the end of the movie that the increased rate of oxygen consumption in the ship is because of the creature's enormous lungs, which leads to the idea of suffocating it by venting all of the air out of the ship. His wife, Mary (Ann Doran), works onboard the ship as the doctor and she, most significantly, discovers the way the creature feeds on its victims when she does an autopsy on Kienholz's body and discovers that every bit of edible fluid in his body has been removed. She also tries to treat the infected wounds it inflicted on Van Heusen and John Purdue but, because of the alien bacteria, she isn't able to do much with the drugs that she has, which leads to them having to go down to the deck where it is and try to get fresh blood to help them (they're successful, but it comes at a major price).
Bob Finelli (Richard Benedict) is kind of the jokester of the crew, remarking early on about how he can't wait to get back to Earth because of how he can't stand being cold, but his demeanor changes drastically when his brother, Gino (Richard Hervey), disappears and is found barely alive in one of the air ducts but isn't able to be saved. He's upset about having to leave him behind and initially says that they should've done something but, ultimately, doesn't blame anyone for what happened. He doesn't much else significant after that, save use his electronics expertise to patch into Calder's spacesuit radio so they can talk to him over the intercom, and try to save him while Carruthers and Royce get fresh blood for Purdue and Van Heusen. That rescue attempt turns out very badly for him, as when the monster breaks out of the reactor room after Van Heusen tries to kill it by un-shielding the reactor, it grabs ahold of him when he tries to climb up the ladder and mauls him to death. There's nothing to say about Gino other than he's one of the first to fall victim to the monster (his own fault, because he stopped to smoke a cigarette), and is found in the air ducts looking very pale and out of it from its feeding on him. Even after he's dead, the monster often drags his body around to continue feeding, including taking him into the reactor room with it.
Maj. John Purdue (Robert Bice) is the one who makes an unsuccessful attempt to save Gino in the air ducts, only to get scratched across the face and later become infected with the deadly Martian bacteria. He feels quite guilty about it, telling Bob that he should've tried harder to save him instead of running for it and that if he wants to blame anybody for it, it should be him, although he also says that, in the end, nothing could've been done to save him. He adds that Gino knew that himself, as he was shaking his head, trying to warn him of the monster when he crawled in towards him. After that, he spends the rest of the movie in pain because of the infection, although unlike Van Heusen, he ultimately survives. Finally, there's Joe Kienholz (Thom Carney), who's only notable for being the monster's first victim when it jumps and slices him up after he investigates its banging around down below. His body is found stuffed in air shaft, with just about every bone broken, but when Mary Royce performs an autopsy on him, she learns that he actually died from having all of the edible fluid in his body absorbed by the monster.
While it's never suspenseful or scary in the least, one thing that I feel It! has over Alien is the feeling of claustrophobia and being stuck in a confined space with something deadly. The basic plotline in both films is inherently scary but, while Alien is infinitely more atmospheric and has a much more frightening monster, the enormous size of the Nostromo there has always diminished the creepiness for me a little bit. While they do have to be on their guard when they go from one part of the ship to another, it's such a large place that their odds of running into the Alien are about 50-50 or less, which hurts some of the suspense in my opinion (not to get off-topic but that's why I felt that the claustrophobic, narrow corridors and rooms of the colony in Aliens made for a more effective setting). Again, It! can hardly be called a suspenseful movie but, that said, I do get a much bigger feeling of claustrophobia because of the size and shape of the ship. Van Heusen says himself at one point, "There's simply no place on this ship for a man to hide," and it's the truth. It's a typical, small rocket-ship, with rather small rooms and quarters, no hallways to speak of, and air vents and ducts that are much tighter and cramped than what you would later see in the sequence in Alien when Dallas is searching the vents, trying to draw the Alien out. What's more, the vertical design of the ship, with various levels connected to each other via ladders, means that when the monster begins stalking all of them, they have to put up barriers between the levels they're on and it's on, slowly but surely running out of places to run to. That's also why Carruthers and Calder have to go outside the ship and re-enter it below the monster in order to set one of their traps for it. It really makes me wish that they'd tried to make this more than just a quickie, B-movie because this environment had a lot of potential.
Visually, the film is well-done, considering both its time and budget (accounts vary but it seems like it was shot in, at the most, two weeks). First off, the cinematography by Kenneth Peach looks nicely crisp and stark in the black-and-white, with lots of good contrasts and shadows, especially in the scenes involving the monster itself. The production design, by William Glasgow and Herman Schoenbrun, while nothing special, as both the interior and exterior of the ship are interchangeable with those seen in most other science fiction films of the time, are well-done and serve their purpose, especially in the claustrophobic sense. And the special effects aren't bad. The surface of Mars, which you see in the opening, the shot of the ship taking off from it, the numerous shots of the ship traveling through space, and the sequence where Carruthers and Calder go outside ship and walk along its side, which is shown in both close-ups and in a big wide-shot with some matting effects, all look pretty good (the way you see outer space outside the airlock door when it opens and behind the ship and actors in the close-up of them crawling out and walking down the side of it is particularly impressive). However, the film's low-budget is apparent in how some shots are reused, such as the monster's shadow when it massacres someone being used for both Kienholz and Bob Finelli's death, and the shots of the ship traveling through space (note how it's always going up and never levels off like it should), and the reuse of dialogue from earlier in the movie. The latter happens when everyone else tries to keep the monster's attention while Carruthers and Calder slip into a level beneath it and, besides it being dialogue that we've already heard, some of it comes from characters who've been killed at this point!
While the title monster has a lot more screentime than the Alien or the James Arness creature in The Thing from Another World, it is similar to them in that you very rarely get a detailed, full-body glimpse of it. For the first bit of the movie, all you see is close-ups of its hands and feet and its shadow on the wall when it's killing someone, and while your first good look at it is when it attacks Purdue in the air ducts when he's trying to save Gino, you still don't get many others of the entire creature afterward. You do get enough to know what it looks like, mind you, as well as some nice, brightly lit close-ups of its face, but for the most part, it's either lit very darkly, sometimes to the point where all you see is a silhouette, or is very far away from the camera. The design of the suit, courtesy of Paul Blaisdell, is pretty cool: it's a humanoid, reptilian creature with big, padded shoulders, three-fingered hands with claws, and webbed feet that are reminiscent of those of the Gill-Man. That said, though, it is very clearly a suit, as you can see the rubber bunching and crinkling in spots and the zipper on the back is plainly visible. The look of the mask is pretty good, although they had a problem with actor Ray Corrigan's chin sticking out through the mouth (which was his fault, since he refused to go to Blaisdell's house at Topanga Canyon, meaning he was unable to take exact measurements of his head when making the suit), forcing them to make it up to look like the creature's tongue. Fortunately, you never get that good of a look at the bottom jaw. Also, the head originally had cat-like eyes but they were removed in favor of using Corrigan's real eyes, which you only really see in one quick shot when the monster is in the reactor room and doesn't hurt the movie at all; in fact, it's kind of startling.
Other than it's being a Martian, the creature's exact origin remains a mystery, although Eric Royce does theorize that it could be of a now extinct civilization on Mars that was destroyed in some way, forcing the survivors to go back to being savage animals. One thing's for sure: it's not only extremely hostile but is vampire-like in that it feeds on the fluids of other creatures, a function that evolution had led it to adopt since Mars is a very barren planet. It absorbs blood, bone marrow, water, etc., any type of edible fluid found in a living body, and according to Mary Royce, it must do this through some sort of osmosis-like process, as there are no bite marks of any kind on the victims. This leaves its victims looking pale, zombie-like, and in the case of Kienholz, whose fluids were completely drained when they retrieved his body, shriveled up. Most significantly, the creature is very strong, able to rip its way through metal, bend gun-barrels completely in half, and easily slice up anyone in its way. Like the Komodo dragons with their bacteria-infested saliva, even if you survive an attack by the monster, you'll still be in danger from infection of a Martian bacteria that normal medical supplies can't combat. Its tough skin and bone structure make it very hard to kill, as it's impervious to bullets, grenades, gas, electricity, and even being exposed to lethal radiation. Ultimately, its enormous lungs, which it developed because of Mars' thin atmosphere and which inhale 40% of the ship's oxygen during the length of the story (which, according to the closing scene on Earth, is only 24 hours, if that), proves to be its undoing, as they let out all of the air and suffocate it.
The downside of the monster is that, nice design and formidability aside, it's not much of a character in its own right. For the most part, it's just a typical, rampaging beast that tears through all of the obstacles in its way and shrugs off everything that's thrown at it simply in order to kill the characters for its nourishment. It has no other goal other than that, and Corrigan, who was an actor and stuntman whose nickname was "Crash" and who retired after this film, doesn't contribute much else in his physicality of the role. In fact, the way he moves around whenever you see him in full-body shots, like when he traps Calder in-between the two pumps, is very awkward and clumsy (when talking about visualizing the Alien, Ridley Scott once said that he didn't want it to look like someone in a dodgy suit bumbling around a set; I wonder if he was referring to this?) There are signs of intelligence in the creature, as you can see it exploring the ship and learning it at some points, and it also thinks to hide its victims, as well as itself, in the air ducts, which is something else that you'd later see in Alien. Finally, its vocalizations consist of deep, growly breathing, loud snarling whenever it's enraged or attacking, growls that grow more and more wheezy and desperate when it's being slowly suffocated at the end, and, most notably, a freakish, guttural howl that tends to echo throughout the ship. When Carruthers is telling Ann of his and his crew's encounter with the monster back on Mars, he mentions hearing a strange sound at one point; I think the look on his face upon hearing the monster's howl when it attacks Purdue in the air ducts makes it pretty obvious that that's the sound he heard, cluing him in that the thing that killed his men is now on the ship with them.
The music score, one of many produced by the partnership of composers Paul Sawtell and Bert Shefter, is pretty standard 50's monster movie music, although there are some notable aspects to it. Save for the very first notes, the music you hear during the opening credits is the same main title that they did for the movie Kronos the year before, but it fits well and, like all great stock music, you'd never know that it originally came from another movie. Significantly, this main title makes use of the xylophone here and there, which they incorporated into the music they produced specifically for the film. One piece that I always remember is this short, building theme with trumpets that you first hear when Carruthers bumps up against an air shaft and Kienholz's hand droops down from up above. The music plays as Carruthers, sensing something, slowly turns around to see it, leading into the entire body slumping down in the duct. The piece that plays when Carruthers recounts his story of what happened to him and his crew early on has a soft, eerie-sounding piece that I like. However, the sound I most often identify with the film whenever I think of it is not exactly score: it's this strange, high-pitched, whirling noise that you hear during the exterior space scenes. Like Carruthers' narration, I'm sure was meant to fill the dead air of those scenes as well as give them sort of mood. It's science-fiction-y in an old-fashioned way but it does the job. Overall, the score isn't bad but it's also far from great; it's simply average. But, that same year, Sawtell would do a much more memorable score for The Fly.