Tommy 46 and wife Tuppence follow dead agent's last words to Sans Souci seaside guest house for male N, female M, Hitler's most trusted to lead Fifth Column. Could they be part-Spanish landlady Mrs Perenna, sulky daughter Sheila, refugee von Deinem, mustached Mrs O'Rourke, bluff Major Bletchley, elderly Miss Minton, invalid Cayley or attentive wife Elisabeth? Surely not Mrs Sprot with lisping toddler Betty?

