Heiress Helen Bradford's lawyer, Scranton, knows that five of her relatives would be richer if she were dead, so he hires detectives Larry Donovan and Budge Edwards to guard her life. Scranton also hires a woman to act as Helen's double in order to determine which of her relatives is planning to kill her. As all five of the visiting relatives have not seen Helen since she was a child, they are easily fooled into believing that the fake Helen is the heiress when they are introduced to her. In addition to planting Helen's double at the estate, Scranton hires Jeanne Martin to act as her maid. The danger to Helen's life soon becomes evident when a hunting arrow appears on her bedroom door. Jeanne sleeps in Helen's room to protect her, while Lobo, a police dog, is nearly killed in an encounter with a prowler. The next day, when Larry, Budge and Helen go rowing, they are struck by an arrow with a note warning that the next arrow will be fatal. After Jeanne and Helen narrowly escape being hit by the third arrow, Reynolds, another undercover detective, who is pretending to be a gardener, is killed just as he is about to reveal the culprit. When the family gathers for the probation of the will, the lights suddenly go out, and, once again, Jeanne is nearly killed. Following the second attempt on Jeanne's life, the recovered Lobo is brought into the room and snarls at Scranton, who is revealed to be an embezzler and Reynolds' killer. Jeanne, it is later learned, is the actual heiress, and she and Budge, who are in love, plan a double wedding with Larry and Helen.