White-knuckle flyer Harry Bittercress, a private eye, is mid-air when a woman who appears to be sleeping is discovered dead — quietly strangled in her seat while no one noticed. With a killer on board, the pilot diverts to the nearest airport: a small city with an even smaller-minded sheriff. His heavy-handed interrogation pins the crime on an innocent man, and when Harry objects, the sheriff arrests him too. That leaves Cardamine, Harry’s sharp-minded and disarmingly charming wife, to take up the hunt. Under her questioning and careful pursuit of clues, passengers who once seemed harmless begin to look less so. Alibis wobble and contradictions surface as Cardamine methodically closes in on the truth. But the nearer she gets, the more perilous it becomes.