Who killed Arnold Armstrong? Anne Watson shoots him with Halsey's revolver, after years in which he extorted money from her over Lucien, the son he fathered on her sister Lucy. Her dying account supplies the direct solution.
What happened to Paul Armstrong? He faked his death in California, substituted another corpse for burial, and returned secretly to recover the bank fortune hidden at Sunnyside. He dies after falling down the circular staircase while fleeing the chimney room.
Who stole the bank's money? Paul Armstrong organized the theft, with Doctor Walker as his principal accomplice. More than a million dollars in cash and securities is recovered from the portable safe.
Why was Halsey abducted? He learned enough to threaten the conspiracy and confronted Walker. Paul, Walker, and their helpers staged a road incident, tied Halsey in a boxcar, and left him there until a tramp found him.
Who is Alex? The gardener is Jack Bailey in disguise. He searches Sunnyside for the hidden assets so he can clear himself and protect Gertrude.
What happens to Doctor Walker? He escapes to South America after the conspiracy collapses, leaving Paul dead and the stolen assets in official hands.
Themes and What the Ending Means
The house as a financial body Sunnyside physically contains the stolen wealth, making architecture an extension of the bank fraud. Walls and chimneys hide what respectable institutions concealed socially.
Independent female investigation Rachel's age and unmarried status free her from the romantic plot's usual restraints. Her curiosity repeatedly advances the case when younger characters choose secrecy.
Different crimes sharing one scene Arnold's murder arises from personal abuse, while the break-ins and later deaths arise from financial conspiracy. The novel warns against forcing every clue into one motive.
Respectability and disguise A bank president becomes a supposedly dead fugitive, a cashier becomes a gardener, and domestic servants hold the family's most dangerous truths.
Comedy as resistance Rachel and Liddy's arguments prevent the threatened household from becoming emotionally passive, turning humor into a form of endurance.