Without telling her family, Lucia Harper drives from her seaside home in Balboa to Los Angeles to warn reprobate Ted Darby to stay away from her seventeen-year-old daughter Beatrice. When Darby agrees to leave Bea alone for a price, Lucia refuses to pay him off, convinced that her daughter will have no interest in a man who would accept that kind of money. Back in Balboa, Bea, who has already spoken to Darby on the phone, does not believe her mother's story and refuses to stop seeing him. Lucia, whose husband Tom is out of town, must handle this problem without his help and forbids Bea to return to art school in Los Angeles. That night, Bea sneaks out of the house and meets Darby in the boathouse, but when he admits that he did ask for money, she strikes out at him in anger with her flashlight. Dazed, Darby stumbles outside and is killed when he falls on top of an anchor. Lucia then discovers her distraught daughter and sends her back to bed. Early the next morning, Lucia finds Darby's body and, not wanting her daughter to be involved in a scandal, dumps the body in the bay along with the anchor that killed him. A short time later, Darby's body is found, but as no one in Balboa knows of their acquaintance, neither Lucia nor Bea are suspected. Lucia believes that she has solved their problems until a man named Martin Donnelly comes to the house and offers to sell her love letters that Bea wrote to Darby. A horrified Lucia is willing to pay the money, but cannot get it without driving again to Los Angeles, an act that would make her family suspicious. When she meets Donnelly the following day, she begs for more time. Donnelly, in the meantime, has become enamored of Lucia, and tells her that if she can raise enough to pay his partner Nagle, he will not take his share of the money. Even so, Lucia finds that she cannot borrow such a large sum of money without her husband's signature. She tries to use her jewelry as collateral, but still cannot get a loan without explaining how she will make the payments. She then pawns her jewelry for $800. When Lucia gives Donnelly the money she has been able to raise, he tells her that one of Darby's shady associates has been arrested for Darby's murder. Lucia is upset, knowing the man to be innocent, and tells Donnelly that she killed Darby. Donnelly does not believe her, however, and advises her that even if the arrested man did not commit the murder, he is guilty of many other crimes. Believing herself to be free of the blackmail threat, Lucia is stunned to discover that Nagle has come to her house to demand his payment. Donnelly overhears their argument and fights with Nagle, killing him. Lucia wants to tell the police everything, but Donnelly stops her, explaining that her resemblance to his mother has made him want to behave decently for the first time. After Lucia leaves to fetch bandages for the wounded Donnelly, he runs away with the body. Lucia and her maid, Sybil, follow and see Donnelly crash the car into a post. When Lucia tries to help, Donnelly hands her Bea's letters and tells her the police will think that Nagle was killed in the accident. He sends a brokenhearted Lucia away, and later she learns that before he died, Donnelly confessed to Darby's murder.