In January 1927 - still recovering from the harrowing circumstances surrounding her disappearance a month earlier - Agatha Christie sets sail for the Canary Islands tasked by the British Secret Intelligence Service with investigating the death of one of its agents whose partly mummified body was found in a cave. One morning Agatha witnesses a woman throw herself from the ship into the sea. Initially nobody connects the murder of the young man on Tenerife with the suicide of a mentally unstable heiress. But Agatha soon uncovers some dark secrets and must use her novelist's talent for plotting to outwit an enemy who possesses a very different kind of evil.