Riding the Stream - Agatha Christie

Gordon Claude was killed in distressing circumstances - by a bomb during the air raids on London - a few weeks after he married a young widow. Overnight, the widow finds herself sole owner of Claude's family fortune.

Shortly afterwards, Poirot receives a visit from my dead brother's wife, who claims to have been warned by 'spirits' confirming that the young widow's ex-husband is still alive!

What will Poirot do?