Bernie Pryde, a private investigator, is found dead in his office. He leaves a suicide tape for his assistant-turned-partner, Cordelia Gray, telling her to take charge. She is hired by James Callender to investigate the 'suicide' of his son Mark. She moves into Mark's old cottage.

Callender's secretary, Elizabeth Leaming, shows Cordelia a home video of Mark, with his friend Andrew Lunn (now working for Callender), and a girl called Isobel. Elizabeth appears transfixed by the image of Mark on screen.

Cordelia visits Isobel, but discovers little. Elizabeth tells Cordelia that she and Mark's mother, Eve, were best friends, and that she helped deliver Mark in Italy. Shortly before his death, Elizabeth gave Mark a prayer book that his mother wanted him to have on his 21st birthday.

Returning to the cottage, Cordelia finds a bolster hanging from the same hook from which Mark's body was found. Cordelia reveals to a policeman that she believes Mark was murdered. She revisits Isobel, who discloses that she found Mark's dead body clad in women's clothes, wearing lipstick. She did not move him, but told Lunn, who later claims he found Mark, as the police did, dressed in men's clothes.

Becoming obsessed with Mark, Cordelia draws lipstick on a photo of him, then attempts to recreate his death by pretending to hang herself. The chair slips and she almost dies, but is rescued by a stray child who is watching at the window.

Cordelia sleeps with Callender. As she tidies the room, she finds a lipstick in his jacket pocket.

Examining Mark's prayer book, Cordelia finds a cryptic message, which she discovers refers to the blood groups of Mark and his parents. The blood groups do not correspond and Cordelia realises something is amiss.

Returning to Mark's cottage, Cordelia disturbs an intruder (Lunn) and is thrown down a well. A car chase ensues. Lunn loses control of the car and drowns.

Elizabeth admits she was Mark's mother, agreeing to the 'business arrangement' so Eve's father would have an heir to his fortune. She concedes that she changed Mark's clothes, and became suspicious when she could not find the lipstick at the scene.

Cordelia and Elizabeth join Callender at the scene of Lunn's death. Callender momentarily mistakes Cordelia for Mark. Cordelia accuses Callender of murdering Mark, saying he wanted to conceal Mark's true parentage and used the women's clothes as an alibi. Elizabeth shoots Callender.