Delphine's sexy spy theme and the fact that Cosima has managed to gather enough information on the clones that her monitor was blindsided.
Helena's cold, steady defiance as she refuses to lure Sarah into a trap.
Mrs. S continues to be awesome.
"Shotgun. Forgot about that."
"That's the lovely thing about this country... Hunting's not just for the rich."
Helena realizing Tomas has been lying to her and that he will kidnap Kira and hurt her if given a chance. She promptly leaps on him and uses all of her assassin training to beating the living hell out of him. It's only thanks to Sarah's intervention that he survives at all.
It's more of a Tearjerker than anything, but Cosima being savvy enough to track down Delphine's true identity, even though it hurt her.
How would you like it if I turned your life inside out?! If I told everyone here that Chad, your husband, slept with the ski instructor long before I did? Well, maybe he acts that way because you BLEW THE ROOFER AT THE CABIN!
Felix's delightful protectiveness of the clones.
Cosima and Delphine collaboratively figuring out the truth behind the Neolutionists' plan, and getting a message to Sarah just in time to stop her signing her life away. Though not in time to save Kira.
Sarah finally killing Helena.
It's understated, but after being kicked out of Cosima's apartment Delphine apparently went home, put her sexy underwear spying skills to good use, discovered the ruse, figured out where Cosima was going, and flew across international borders (nobody knows exactly where Sarah lives, so it could have been anywhere from a half-hour flight to the entire continent) to show, rather than tell Cosima exactly what Leekie was up to. She did all this without even bothering to change her clothes at any point. And it's Delphine who first realizes the code is binary.
In hindsight Donnie not cracking under Alison's torture and convincing her that he wasn't her monitor. It's as impressive as it is heartbreaking.