Murder in Vienna by E.C.R. Lorac

Superintendent Macdonald, C.I.D., studied his fellow-passengers on the Vienna plane simply because he couldn't help it, because he hadn't conditioned himself to being on holiday. The distinguished industrialist he recognised: the stout man he put down (quite mistakenly) as a traveller in whisky. The fair girl was going to a job (he was right there) and the aggressive young man in the camel coat might be something bookish. Macdonald turned away from his fellow-passengers deliberately: they weren't his business, he was on holiday--or so he thought.

Against the background of beautiful Vienna, with its enchanting palaces and gardens, its disenchanted back streets and derelicts of war, E. C. R. Lorac constructs a detective story with all its complexities; an exciting and puzzling new crime story.