halsey and gertrude innes, along with gertrude's fiancé jack bailey, visit their aunt ray who is leasing banker paul armstrong's home for the summer. aunt ray finds arnold armstrong, paul's son, dead at the foot of the staircase and suspicion falls on jack since he is arnold's business enemy. lousie armstrong, who is travelling with her dad, is found hiding and dazed. the house keeper, mrs. watson, develops blood poisoning and falls down the stairs. soon after, news arrives from armstrong's bank, which was recently robbed, that armstrong has died. mrs. watson confesses to shooting arnold because he had beat her with a golf club. aunt ray accidentally discovers paul armstrong hiding in a secret room and screams, alerting the others. detective jamieson and the new gardener alex pursue armstrong. during the chase, armstrong slips and fatally falls down the stairs. it is revealed that alex was actually jack in disguise trying to clear his name. gertrude embraces him, and louise hugs halsey.