From The White Feather: When an anti-Semite asks Foyle if he's Jewish and Foyle refuses to play his game.
In most episodes, Foyle delivers a comprehensive verbal smackdown to the criminal who he's tracked down. And out of all of them, the one from Fifty Ships is probably the best:
Foyle: You know, I sometimes wonder why I do this job. And then I come across someone like you. I mean, we're living in such evil times, when the whole world seems to be sinking into some sort of mire. And as if Hitler wasn't enough, we've got the likes of you, who capitalize on other people's misery, who hurt them, make things even worse for them when they're at their weakest. And it's with the likes of you that this mire begins. And it's some small consolation to know that I've helped to clean up just a little bit of it.
One of the many Karma Houdinis in the series, an American businessman who is instrumental in a movement to bring America into the war, is about to hop on a plane when Foyle 'asks to say goodbye'. The businessman smugly gloats about it, leading Foyle to calmly retort that it's the war that's keeping the businessman from receiving punishment — but wars end, and when this one does the businessman will still be a proven murderer, and Foyle still has the proof that he's a murderer: "You're not escaping justice. Merely postponing it. Au Revoir." The businessman suddenly looks a lot less pleased with himself.
At her new job in a map-making facility, Sam Stewart overhears a potentially incriminating conversation between a suspect with something to hide and another party. That night, she's preparing to go home when the suspect suddenly appears behind her, suggesting that it'd be a lot healthier and safer for her if she just forgot about the whole thing. Sam calmly replies that she'd actually forgotten about the whole incident, "but since you're so worried about it you've come out here to try and bully me, I'm going to mention it to everyone I can." She then rides off without a backwards glance, leaving the suspect gobsmacked.
After the attempted bombing of a gasoline depot (and Sam) with a suitcase bomb, Foyle takes the suitcase and brings it back to the bomber, causing the bomb-maker to freak out when he recognizes the suitcase. His reaction to the suitcase in front of witnesses proves he built the bomb that went in it. The bomb-maker talks when he realizes he's unintentionally confessed, giving up the rest of the petrol-smuggling ring the bomb was set to cover.