Name one show that does not strain credibility
All of the great ones (though none are perfect - Breaking Bad lost me a bit with the train heist this year, and the physics of the electromagnet really do not add up either).
The very unlikely can be presented in a way to make it seem believable in the larger context of the fictional universe created by the show.
If I said "British ad exec gets run over by a lawnmower at an office party and blood sprays everywhere'", you might say that lacks credibility. But in the context of Mad Men, it was totally believable (and will never be forgotten by any who saw it).
Sherlock Holmes sneaking into a terrorist cell dressed up in a burka, and wielding a scimitar to behead a woman smelled like complete bullshite, even in the "Sherlock" universe (where a lot of amazing things happen). Good writing can make the improbable happen. That episode just had one too many twists.
LOVE the show overall, though.