A light country-house mystery follows a group of young socialites whose practical joke yields a corpse and exposes a covert club identified by a seven-point emblem. Amateur sleuthing, furtive meetings, and a missing scientific formula escalate the amusement into international intrigue. Parallel investigations by a methodical superintendent disentangle false alarms from deliberate deceit, reveal a spy network, and recover the stolen material, while episodes of comic misadventure and social satire punctuate the unfolding puzzle.