Instruct: Classify Amazon reviews into positive or negative sentiment
Query: How a criminal takes advantage of wartime conditions.

"Enemy Unseen" was written during World War Two. Detective Inspector French of Scotland Yard is wondering "why war conditions had not been more widely taken advantage of by criminals". Just such a crime then comes to his notice. Coils of wire and boxes of hand grenades are reported missing from a Home Guard ammunition store at a Cornish coastal village. Soon after an explosion on the beach nearby kills an old man, and later there is a similar murder.This is a grimmer, more static mystery than Crofts usually provided, no doubt reflecting the harsh "war conditions" in which it is set and written. One of the characters is a writer of detective fiction. He provides illuminating views of the craft of which Crofts was a master.