The peaceful setting of the St. Aubyn family estate, known as Bastions, on England's Cornwall coast, masks the troubled state that exists within its walls. It is to this estate that Sherida Binyon (Phyllis Thaxter) has been summoned for a one-month trail employment as a personal secretary to the wheelchair-bound poet Leah St. Aubyn (Susan Peters), who writes popular sentimental verse using the pseudonym Faith Hope.
Soon after arriving at Bastions, Sherida is introduced to Leah's husband Mallory (Alexander Knox) and her three stepchildren, Jane (Allene Roberts), Christine (Peggy Ann Garner), and Logan (Ross Ford). It is only when Sherida meets Leah that she discovers Leah is confined to a wheelchair. Mallory later explains to Sherida that Leah had rescued Logan and Jane from drowning at Echo Cove on the cliffs beneath the house near the sea. In the process of the rescue, Leah was swept out to sea and dashed unto the rocks, where her back was broken, crippling her. Leah appears to have adjusted to her inability to walk and presents a smiling face to the world, a face reinforced by the optimistic poetry she publishes.
As Sherida settles into her new duties, Leah continues her flirtation with her physician, Dr. Simon Crowdy (Ron Randell). Simon, however, is in love with Jane and had just asked her to a country club dance. Leah had given her approval.
Later, Simon tells Leah he intends to ask Jane to marry him, even though she is younger than he is. But Leah orders Simon's not to do this, whereupon she is subjected to a frank analysis of her problems by the doctor. Simon tells her that she is exhibiting obsessions typical of those born under the astrological sign of the ram, Aries. He also accuses Leah of conditioning Jane to cling to her out of a perverse need to keep her "band of slaves intact. Love can be selfish, too, particularly if it hurts other peoples lives."
Stung by Simon's words, Leah exacts her revenge by lying to Jane, telling her that Simon confided in her that he thought Jane was getting too serious about their relationship and that Jane was too young for him. Jane decides not to go to the dance with Simon and withdraws from his company.
Stepdaughter Christine, the youngest of the three children, has an unnaturally close attachment to Leah. Leah doesn't discourage this closeness, though Leah is not above making an occasional hurtful comment to Christine--sending her away when Christine wants to be with her, threatening to send her to boarding school, and so on. On one occasion when Leah is faking an illness in order to get Dr. Crowdy to the house, Christine becomes hysterical, sobbing and shrieking, when Mallory won't let her into Leah's bedroom. Sherida steps in, grabs Christine, and shakes her to bring her back to reality. Christine's suspicions and dislike of Sherida begin here.
After destroying Jane and Simon's relationship, Leah next drives a wedge between Logan and Catherine Woolton (Diana Douglas). Logan and Catherine had been childhood friends and then had a romantic attachment to each other before Catherine left for Paris, where she studied painting. Logan had studied law in London. Catherine has become a successful artist; her paintings are beginning to sell. She's come back for a stay with her adopted parents, the local vicar, Reverend Woolton and his wife (Gerald Hamer; Doris Lloyd). Together again, Logan and Catherine rekindle their romance; Logan asks Catherine to marry him, and she eagerly agrees. They plan to be married at once, after which they will live in London.
The couple announces their betrothal, which Leah says she approves of, and a ball is given in their honor. But at the betrothal ball, Leah talks to Logan and Catherine, telling them very firmly that she wishes them to postpone their marriage for at least six months, and preferably a year. Both are angered and puzzled by Leah's request, yet Logan reluctantly agrees to a postponement.
Shortly thereafter, while Logan is gone, Leah summons Catherine to the house and tells her that she knows who Catherine's parents are. Catherine is astounded by this information because she says that she was a foundling and even her adopted parents do not know who her birth parents are. Leah, nonetheless, tells Catherine she has uncovered her parents' identity and learned that Catherine's birth father was insane. That is why she asked Logan and Catherine to postpone their marriage. With an insane father as part of Catherine's family tree, Leah suggests that Catherine may not want to marry Logan after all because, if she did marry Logan, they should not have children. And Leah isn't sure that Logan would want a childless marriage.
Catherine all too readily believes Leah's claims. Then Leah tells Catherine that Logan fled to London after learning that there was insanity in her family. Devastated by Leah's words, Catherine vows never to see Logan again, and then disappears. Her disappearance is soon explained by a suicide note that the Wooltons find. A search for Catherine leads Mallory and others to Echo Cove, where Mallory is able to rescue Catherine from death in the waves.
Meanwhile, in London, Logan had investigated claims that Catherine's father was insane. But Logan was unable to discover any records that revealed who Catherine's parents were. Logan now knows that Leah lied in an attempt to break up their relationship. He hastens back to Bastions, to discover Catherine ill in bed after being rescued from her suicide attempt. He reassures Catherine of his love and tells her Leah's story was a lie. Both Logan and Catherine vow never to return to Bastions.
Meanwhile, the confused Christine, believing that Sherida is the source of the family's troubles (on no other grounds than "that all our troubles began after she came here") attempts to kill Sherida by loading a glass of warm milk with sleeping pills and then taking the glass in to Sherida just before Sherida goes to bed. When a servant alerts Mallory to the fact that Sherida is unconscious, Dr. Crowdy is called, and Sherida is revived.
Mallory has discovered that Christine was the culprit. Malloy gives Christine a lecture, explaining that she's too insulated at Bastions, that Bastions isn't the world, and she must get a larger view of life. Mallory blames himself for not providing Christine with this larger view. Rather quickly, Christine begs Sherida's forgiveness (and gets it, naturally), has a change of mind, and tells Leah that she is going away to boarding school.
Mallory and Leah talk, and it becomes apparent to Mallory that Leah thinks he's in love with Sherida. He insists that he is not but walks out on Leah when she will not believe him. Now bereft of all her children (Jane and Dr. Crowdy have come together and plan to marry) and husband, Leah wheels herself to the edge of an ocean-side cliff and throws herself over to her death.