In this espionage drama, a Secret Service agent must discover who has been smuggling British arms into China. The prime suspect is a prosperous Chinese merchant-philanthropist and the agent thinks the merchant is working with the notorious Chinese guerilla warlord General Ling.

Private eye Slim Callaghan is summoned to the country home of a Colonel Stenhurst, but the latter is murdered before he can talk to the detective. Was one of the Colonel's three daughters responsible?