I just finished watching the three seasons of
The Tunnel. It's pretty amazing and well done. I love the characters. It begins with a dead body being found in the middle of the channel tunnel in such a way that the French and English police are obliged to work together on the case. Yes, the premise seems very artificial, but it works. And of course you wonder how they could extend the premise to a second and third (and definitively
last) season, but they do.
The main characters are played by Stephen Dillane (who was Stannis Baratheon in
Game of Thrones) and Clémence Poésy (who was Fleur Delacour in
Harry Potter and the Deathly Hallows). Dillane is really good in this, but Clémence is not to be missed. Her character is one of the best fictional detectives that have been created, IMHO.