Blood Oath was an unexpected episode. It didn't set out to celebrate any anniversary, nor was it featuring a massive star from another series, but it ranks up as being one of the best crossover episodes in the franchise because it took not one, not two but three Klingons from The Original Series Kang, Kor and Koloth and wrote them into Dax's backstory. The episode has an emotional backbone as Dax must decide essentially whether she would be willing to commit murder in the name of vengeance, and the silent scene at the end with Sisko and Kira was very emotional and well played by all the actors involved. All three Klingons were played by their original actors and it was brilliant to see William Campbell in particular who may be better known as portraying Trelane. Even if we hadn't seen the three Klingons before, this would be a brilliant episode with a real moral to the tale. Up until now we hadn't seen a great deal of Klingons on DS9 and this redressed the balance. We only got to see Koloth and Kang here, but we got two further episodes with Kor and both of those were good too.
