The Double Clue (S03E07)

Japp, anxious that a botched investigation could jeopardize his career, requests Poirot's assistance in solving a string of jewel heists. During the investigation, Poirot becomes enchanted by the astute and captivating Countess Vera Rossakoff, who also happens to be a prime suspect. As Poirot dedicates his time to her, Hastings and Miss Lemon take the lead in uncovering the case's intricacies. Ultimately, this investigation may be remembered as the elusive case that slipped through their fingers.