How many Tommy and Tuppence books did Agatha Christie write?

Dame Agatha Mary Clarissa Christie, DBE (née Miller; 15 September 1890 – 12 January 1976) was an English writer known for her 66 detective novels and 14 short story collections, particularly those revolving around fictional detectives Hercule Poirot and Miss Marple. In 1971, she was made a Dame (DBE) for her contributions to literature. Guinness World Records lists Christie as the best-selling fiction writer of all time, her novels having sold more than two billion copies.

Tommy and Tuppence are two fictional detectives, recurring characters in the work of Agatha Christie. Their full names are Thomas Beresford and his wife Prudence. The first time Tommy and Tuppence appeared in a Christie novel was in 'The Secret Adversary' (1922). The five Tommy & Tuppence books by the mystery writer, are 'The Secret Adversary', 'Partners in Crime', 'N or M?', 'By the Pricking of My Thumbs', and 'Postern of Fate'.