In New York, Steve Clark, a mostly unemployed private investigator, receives a phone call from Bill Emerson, who runs Escort Service Inc., for which Steve occasionally works as a male escort. Bill assigns Steve to escort Mrs. Ava Eastwood, a very wealthy, Park Avenue widow for a week. However, before he can begin the job, a young woman comes to his hotel room, seeking his help and stating that Eddie Rocco, a friend of Steve’s, had recommended him to her. During her visit, the phone rings and when she learns that the caller is Mrs. Eastwood, she runs off. That evening, when Steve meets the young, attractive Mrs. Eastwood, she explains that she wants him to escort her stepdaughter Karen, whose father was recently killed in a horse-riding accident. Karen has become withdrawn and Mrs. Eastwood thinks that she may be using narcotics. Mrs. Eastwood asks Steve, who will be introduced as an old friend from her hometown of Chicago, to try to revive Karen’s interest in people and events. While Steve and Mrs. Eastwood are talking, Karen returns home and Steve discovers that she is the young woman who had earlier visited him, but pretends not to know her and says he will phone her the next day. Later, however, Steve finds Karen in a bar and, by tricking her, learns that she is not using drugs. After Karen accuses him of being in league with her stepmother, Steve visits Rocco, the bar’s owner, to ask why he had suggested him to Mrs. Eastwood, but Rocco replies that he simply felt that Steve was best qualified to help. When Mrs. Eastwood comes to Steve’s hotel room, she reveals that she and Dr. Parks, the family’s psychiatrist, have reason to believe that Karen killed her father by sabotaging his riding tack. Mrs. Eastwood, who was formerly Karen’s father’s secretary, explains that Karen intended only to injure her father and by nursing him back to health, wean him away from her stepmother. After Steve tells Mrs. Eastwood about Karen’s visit and his concern about the odd coincidences, she seduces him. Steve then receives a phone call from a man offering to sell him information about Eastwood's accident and they arrange to meet out in the country. Later, Karen visits and tells Steve that she believes that her stepmother married her father for his money, then threatens to shoot Steve, but he easily gains control of her gun. At the rendezvous site where Steve is to meet the informer, an unseen assailant knocks him out with a sap. When he recovers, Steve discovers the informer’s dead body, shot by Steve’s gun, and realizes that he is being framed. After Steve relates his adventures to Bill, he drives to the Eastwoods' riding stable and, in the tack room, finds a cut strap on Eastwood’s saddle. When Rocco tells Steve that the murdered man was a disbarred jockey, Steve suspects that Rocco might be involved, but Rocco insists that he is an innocent party. Steve then visits Dr. Parks, who tells him that he believes that Karen killed her father and, although Karen remembers nothing of the day of the accident, he and Mrs. Eastwood are planning to send her away to a sanitarium for a lengthy treatment. Karen visits Steve again and tells him that she does remember most of what happened on the day of the accident. She saw her father fall, but then blacked out. Rocco, who has been doing some investigating of his own, tells Steve he thinks that Mrs. Eastwood planned the “accident” and is trying to incriminate Karen so that she can keep all the insurance settlement. Steve then arranges to have all the principals meet at the stable. Bill is to bring Karen, but arrives alone and suddenly draws a gun on the group, then asks Steve to explain his theories about what happened. Steve explains that whoever cut the strap also accidentally cut himself or herself. Steve then tells Bill, who has a bandage on his hand, that he has checked on his background and discovered that he was formerly married to Mrs. Eastwood. Bill had introduced Eastwood to his wife and they had planned the whole scheme to collect the insurance money. Steve then tells Bill that Mrs. Eastwood intends to double-cross him and leave with Dr. Parks. After Mrs. Eastwood and Parks admit their relationship, Bill shoots her and runs off. Steve chases him along a railroad track to a high water tower, which they both climb. At the top of the tower, after Bill shoots Steve, wounding him, he heads back down but, as police close in, he falls to his death.