In January 1927 - and still recovering from the harrowing circumstances surrounding her disappearance a month earlier - Agatha Christie sets sail on an ocean liner bound for the Canary Islands. She has been sent there by the British Secret Intelligence Service to investigate the death of one of its agents, whose partly mummified body has been found in a cave. Early one morning, on the passage to Tenerife, Agatha witnesses a woman throw herself from the ship into the sea.