The movie opens with an oblique aerial view of The Maze of hedges and a pond to mark its center at Craven Castle in Scotland. A simple wooden door, marked "Keep Out," swings open and title and credits roll over the bushes that make up the entry to The Maze. A light, high up in a single window of the castle shines. A man, William (Michael Pate) opens the window and calls to his co-worker, Robert (Stanley Fraser) who runs back into the castle. They discuss their master and walk back up to the tower room. As they discuss the options over the dead body of Sir Samuel MacTeam we hear a shuffling sound. Much of the story is told as a flashback by Edith Murray (Katherine Emery). Aunt Edith tells us it happened in a remote castle in Scotland. It started a year before when she and her niece gathered in the south of France at Cannes for an engagement party. Seated in the restaurant was Richard Roblar (Robin Hughes), the soon to be best man. To his right is Kitty Murray (Veronica Hurst), then Aunt Edith and finally Gerald MacTeam (Richard Carlson) on the far right. Richard and Kitty dance, this leaves Gerald and Aunt Edith alone to discuss the castle. Gerald explains that no improvements or modern conveniences have been installed in hundreds of years: no electricity, no phones, and no central heating. He also discloses that his uncle locked him in his room every night and the outdoor maze was off limits. The wedding is to take place in two weeks. Gerald and Kitty dance, leaving Edith at the table alone. Edith recounts that none of the Baronets lived but a few years after inheriting the title and Gerald was the next in line. The next day Kitty and Gerald are enjoying the pool at the hotel. A waiter brings Edith an Express Letter for Gerald from Craven Castle. She hands Gerald the letter after he and Kitty exit the pool. The letter provides few details, but it is from William and he says it is urgent he return to the castle immediately. Gerald decides to take the noon plane for London and return as soon as possible.A week has passed and Kitty and Edith check the hotel mail for any word from Gerald. Kitty expresses her concern, "I'm worried about him. Something's wrong, I'm sure of it." She decides to telephone, but Edith tells her niece that there are no telephones at the castle. Kitty decides to send a cable. Kitty shows her aunt a newspaper story, "Scottish Baronet Passes." It further explains, "Sir Samuel MacTeam, Bart., died at Craven Castle, Scotland of a heart ailment this past weekend. He was forty-five years of age. Sir Gerald MacTeam, his nephew and successor as Baronet, has announced that the burial services will be private." Edith and Kitty are relieved now that they know the reason for Gerald's silence. Kitty learns that all her cables were received at the castle, but none answered. Edith is convinced that Gerald is no longer interested in her niece, and advises, "Forget him, Kitty." Kitty convinces herself that Gerald must be in trouble and unable to reply. Six weeks later Edith, not Kitty, gets a letter from Craven Castle. She opens it with Kitty present. Gerald is vague as to the reasons, but makes it clear he will not marry Kitty: Only a death could make him reconsider. Kitty decides to visit the castle and confront Gerald and invites Edith to accompany her.A driver brings the pair to the castle. He drops off their luggage on the road and drives off without a word. The women carry their luggage to the front door and knock. William, a gray haired man, answers the door carrying a candle. When told the Baronet is indisposed, Kitty pushes her way into the castle and demands that Sir Gerald be summoned. Edith expresses her reservations, "Kitty, we should never have come here. And the sooner we leave, the better." Gerald walks casually down the stairs. Kitty runs to greet him, but stops short when she sees that in less than two months, since she last saw her fiancé, he looks to have aged twenty years. Rather than expressing how glad he is to see her, he tells her, "You shouldn't have come here." He demands that Kitty and Edith leave at once, but Kitty informs him that they will be staying. Gerald orders William to take the ladies to one of the bedrooms. The ladies walk upstairs to their rooms, but before they are out of sight, Gerald tells them, "I expect you to leave in the morning." William takes the ladies to a large bedroom with a connecting door to an adjoining bedroom, so each will have a bed of their own. He lights a candle and then the fireplace. Kitty is shocked and expresses her concern to Edith regarding Gerald's appearance. They are even more surprised by his inhospitable reception. Gerald sits and drinks and reminds William about the time. He glances upwards, then to William and asks what bedroom they occupy. Williams reminds Gerald that Robert will lock both their bedroom doors. Kitty and Edith sit by the fire and drink tea. Kitty notices that the window in her room has been sealed up with stones. She also notes that all the hallways have rubber coverings and that the stairs are a series of platforms, instead of steps. Edith says, "Everything about this place is strange. I can't tell you how delighted I shall be to leave it." But Kitty insists they will not leave until she has a chance to do something to help. She is convinced that Gerald's appearance alone is reason to believe he is sick. Edith tells her niece, "Kitty, whatever has happened to Gerald is something evil. I can feel it in this place. And we have to get out of here before it happens to us." They hear the door being locked. Despite protests from the women to unlock the door, Robert leaves. Edith tells Kitty about the castle rules as Gerald had told her in Cannes. Before Gerald can walk upstairs, William tells him the cleaning woman who had an attack the week before has died. She apparently died as a result of going into The Maze, despite warning to stay out. Gerald walks upstairs to the tower room.Kitty awakens during the night. She hears a strange shuffling sound out in the hall and sees only a partial shadow under the door. She sees the tapestry on the wall move and pulls it back. There is a door that leads to a very old and dirty stairwell. She claws through cobwebs and is menaced by a couple of bats. She climbs the stairs to a window; one pane is broken. Outside she can see The Maze and the bright spot of a moving candle lighting the shrubs. Again she hears the curious shuffling sound. She returns to her room and immediately wakes her Aunt Edith and tells her about what she saw. Edith reiterates her desire to leave and the sooner the better. The next morning the door is unlocked. Kitty checks on her aunt and finds she has a cold. Kitty uses it as an excuse to remain. Kitty notices strange footprints on the stairs, almost like leaf impressions. Robert catches her and immediately wipes them off. Kitty joins Gerald at the dining room table. Kitty informs Gerald that Aunt Edith is sick and it will be at least three days before they can leave, but Gerald insists the two women leave this morning. Kitty confronts Gerald about his behavior and reiterates her desire to help. Kitty asks William to get a doctor for Gerald, but he politely refuses. Kitty proposes a friend, an M.D., visit and examine her fiancé and writes a letter to Dr. Bert Drilling. Robert sees Kitty composing a letter and informs William. Before she seals the letter she reads it to Edith. The next problem is to get it posted: For that she engages the gardener, Simon (Owen McGiveney), refusing to allow William to do so after he volunteers. Kitty wanders into The Maze. She only gets in a few dozen feet when she notices the same curious footprint, if that is what it is. She crouches down to get a better look when Gerald stamps his foot down and destroys it. He grabs her arms and escorts her out of The Maze and snarls, "Stay out of here for the rest of your visit." Kitty tells her Aunt Edith the story and Edith decides she will have a talk to Gerald, but she is put off by the staff. During the evening lock down, Edith leaves her room first. She follows the staff upstairs quietly and at a discrete distance. She enters the tower room and hears the shuffling sound. She only catches a glimpse of a man-sized creature shuffling away. She screams, faints, and falls to the floor. Kitty is awakened by the scream and runs to her aunt's room. Gerald carries Edith to her bed; he is accompanied by William. When Edith comes to she tells everyone, "Gerald. I went to your room and I saw something. Something horrible. It was the most horrible thing I'd ever seen...It was something alive, I saw it move." Gerald dismisses it as imagination.Later that night Kitty is again awakened by the shadow under the door and strange shuffling sounds. The next morning Kitty checks on Edith. Gerald asks if Edith is better. Again Gerald insists they leave and Kitty promises to leave the next day. That afternoon, the guests Kitty expected arrive. Richard Roblar drove the car, along with his girlfriend, Peggy Lord (Hillary Brooke). In the backseat is Dr. Bert Dilling (John Dodsworth) and his wife, Margaret (Lilian Bond). Gerald is at the table reading a book entitled, Teratology. He hears the commotion outside and walks out to see. Kitty has already greeted her guests when Gerald comes outside. He looks daggers at Kitty. Kitty informs Gerald that their friends would like to rest before dinner. Gerald pulls Kitty aside and reads her the riot act. Kitty appeals to Gerald and begs to help, but he informs her, "I'm not ill, Kitty. I only wish it were that simple." She picks up the book and leafs through it, but Robert enters the room and takes it out of her hands. Kitty goes to see her guests and asks Bert what he thinks. Bert doesn't think it is physical, despite Gerald's appearance, but mental. Kitty and Edith dress for dinner, and then join the others for drinks. While everyone is laughing and having a good time, Gerald stands by the fireplace with a pained expression on his face. A noise upstairs causes Gerald to bolt the room. Bert decides to act. He tells Kitty that he will complete the necessary paperwork and have Gerald committed. Gerald returns with Robert and William and dinner is served. Kitty asks Edith to steal a key from the door so she can get out during the night. Gerald announces that everyone be in their rooms by 11:00 p.m. and that they all leave in the morning.While his wife, Margaret, gets comfortable in bed, Bert paces his room. He informs Margaret that he will shoot the lock off the door if necessary. He also tells her he did his research on the MacTeam family and it was all very strange. William informs Robert that the key from the great hall is missing, but since it is 11:30 they have other more pressing duties. Kitty takes the key and exits her room with Edith. They start up to the tower room and unlock it with their purloined key. The tower room is sparse but the windows are not blocked off. They find a piece of seaweed on the floor. They find the book. The title page explains that Teratology is, "The Study of Monstrosities, serious malformation or deviations from the normal structure in man." They hear the strange shuffling sound and quickly exit the tower room. Gerald leads a procession holding a candle. Robert and William carry a sheet that hides the shuffling thing beneath. Kitty and Edith return to their room. Kitty decides to follow the procession. Outside her room she discovers another 4-toed footprint that resembles a tree leaf. She also concludes that whatever the creature is, it is a person. She notes that Sir Gerald addressed it as "Sir." Kitty and Edith walk outside and into The Maze. They hear a splashing sound. They get separated from each other and lost when the candle goes out. They desperately try to find each other, calling and wandering. Edith confronts the creature and screams. Kitty encounters it also: A giant, man-sized toad, mouth gaping open, leaps towards her. Both frightened, they flee from each other. The giant toad exits The Maze and hops and crawls back to the house. Gerald finds Edith and orders his servants to attend to "Him." Kitty finally finds Gerald and her aunt, while the giant toad makes his way up to the tower inside the castle. Bert hears the noise of the toad and using his gun on the lock, escapes his room. As Bert exits his room he sees the creature and hears its elephant-like trumpeting. Williams prevents the doctor from shooting the thing as it hops upstairs. Gerald escorts Kitty and Edith back to the house, but bolts when he hears the trumpeting. The giant toad flings itself out of the tower window and crashes to the ground below. Gerald kneels next to the creature. William explains, "He was frightened. I tried to tell him that he was safe but he wouldn't listen, Sir Gerald. When he tried to climb out of the window he was too strong for us." Gerald assures his servant it was not his fault and directs him to carry the body inside.The next morning Kitty packs her bag. Edith is ready to leave. William informs the pair that Gerald wants to see them in the dining room. All the guests are waiting there. William also informs them that Sir Gerald is now the master. Gerald joins his guests. He sounds more like his old self. He explains that for the last few hundred years he and his ancestors were not the actual lords of Craven Castle. The real Baronet died last night, and was born in 1750. Naturally, his guests are incredulous. Gerald explains that certain amphibians can live over 200 years. He tells his guests that human embryos go through many stages. One is an amphibious stage, and Sir Roger never physically developed beyond that stage. The nephews took care of the Baronet for hundreds of years, but he administered the estate. Gerald assures Kitty it was not her fault for the death. He reconciles with Kitty. Edith explains that the two are married now and that Gerald has modernized the castle. We close with a zoom-in shot of the grave of Sir Roger. The headstone reads, "Here lies Sir Roger Philip MacTeam, Bart. of Craven 1750-1953."