The American novelist Alma Katsu spent 35 years as an intelligence analyst for the US government. But after six acclaimed novels, she’s now known as the Queen of Disasters, taking real events and re-imagining them – with added supernatural elements. Her new novel The Deep gives an eerie, psychological twist to the sinking of the Titanic, and the fate of her sister ship the Britannic. Alma Katsu talks to Rob Weinberg about how she turns real life tragedies into supernatural fiction.