Why Didn't They Ask Evans?

S4 E4: As the sole witness to a dying man’s last words – “Why didn’t they ask Evans?” – Bobby Attfield is determined to solve the riddle they pose. Forming an unlikely alliance with socialite Frankie Derwent and visiting family friend Miss Marple, his resolve is strengthened when someone tries to kill him. A trail of clues leads them to Castle Savage and its inhabitants.