Apart from the actual premise and the climactic scene where the monster is wearing the stupidest Halloween store mask you've ever seen in a movie released by a major studio, it's surprising how seriously the actors, script and direction by Roy Del Ruth take this atomic age shocker.

Everything about it makes it look like camp classic but – to the extent the narrative allows her to – Beverly Garland believes completely in her role as a frantic woman who's fiance has run out on her and prompted a one-woman manhunt to find him again.

There's a bookending device where two psychotherapists are discussing the pretty assistant who works for one of them, how she has all the appearances of being competent and stable, but how some bad psychological trauma has made her shut out an entire recent episode in her life.

She agrees to submit to a medical treatment intended to let her accessing her memories while she's barely awake, so she can tell them what happened to her.

As she does so we cut to the story of what actually happened to Jane (Joyce, as she was known before and has forgotten). She's boarded a train with her beloved husband to be, Paul (Richard Crane) and they're blissfully in love, but when he opens a telegram that's delivered mid-journey, his face falls, he tells her he loves her and that he's sorry and he gets off the train, disappearing into the night.

Over the next few months Jane tracks Paul down to a town in the swampy deep south of Louisiana from old papers, and when the train drops her off at the end of the line she notices a delivery man collecting cargo from the train who's going to the plantation she intends to visit to search for her husband.

He accompanies her but she's horrified at his hatred of the alligators that are found in the local landscape, hurrying into the house when they arrive to get away from him. The mistress of the plantation, Lavinia (Frieda Inescort) is cold and barely welcoming, and when Jane presses her too hard about Paul's history there she insists Jane leave.

But the last train has left, giving Lavinia no option but to invite the younger woman to stay the night, telling her she has to leave in the morning. The night brings even more clues (and horror), such as when Jane awakens to the sound of the drunk deliveryman standing out in the swamps shooting at alligators. Even the maid secretly advises her to leave, alluding to some tragedy that's befallen the house.

Meanwhile, there's a nearby lab where a doctor conducts experiments on bandaged patients, something to do with the canister of radioactive material the driver has collected from the train station. He knows Lavinia and what's more, they talk in hushed tones about how they have to get rid of Jane before the secret of their whole operation is blown.

Jane has refused to leave, convinced the occupants know more about Paul than they're letting on. She's awakened from sleep the following night by piano music and surprises the player when she investigates, who flees and leave muddy claw prints through the house.

Even though she has no idea why he fled from her, Jane becomes convinced it's Paul skulking around, and Lavinia finally breaks down and confesses. Paul is her son, and he refuses to see Jane because of what he's become thanks to the doctor's experiments.

The plane crash Paul suffered as a military pilot has already been referenced in the train scene, with Jane marvelling at how well Paul recovered from his injuries. Turns out the local doctor, in cahoots with the plantation owner, has developed a serum that gives people the power to regenerate limbs like alligators and lizards. But it's gone wrong, and the telegram the loved-up couple received on the train was warning Paul about what he'd become – horribly disfigured and covered with scaly, reptilian skin.

Here's where it goes a bit ridiculous, with the delivery guy taking Joyce captive after rescuing her in the storm she was running through to pursue Paul, Paul having to rescue her and bring her back to the lab, insisting the doctor give him an uncut does of the radiation, hoping it cures him for good. Being a 50s B movie, things don't go to plan.

If you watch it hoping for camp thrills and even laughs, you might be disappointed. There are some well staged outdoor scenes (or at least, very well dressed indoor scenes complete with live alligators) and Garland sells it every step of the way, giving it more serious emotional stakes than you usually see in films of this genre and this era.