What a hilarious episode! I did find the premise of Leonard getting involved with Raj's sister a bit weak, but the way the show ran with it was brilliant.
The real fun began when the four friends started arguing over who had lied, cheated or betrayed the others the most. Every confession made things worse, and I was laughing at how quickly they turned on each other. The writing was sharp, and the actors made every line land just right.
Sheldon's elaborate attempt to cover for Leonard was another highlight, especially because he seemed completely unaware of how ridiculous the whole thing was. But for me, the best part was that argument between the four friends, with everyone trying to defend themselves while exposing someone else.
8/10: The episode may not have started with the strongest setup, but it delivered laughs almost all the way through.