O'Neil and Chaykin deliver up the last full-length Fafhrd and Gray Mouser story in Sword of Sorcery 3 (July/Aug 73).
The two men start of the story shipboard. They are just passengers, but still wind up in battle when the ship gets raided, and woman who has been hidden on board by the captain gets captured.
Returning to land, they seek out the man they believe ordered the attack, only to find they are in a far more complicated plot. The leader of the realm is dealing with a rebel, and his own forces have been deserting him. He requests Fafhrd and Gray Mouser go after the rebel and retrieve the captured princess. He has no troops or ships to offer them, but does have a wizard.
The wizard is really far more of a scientist, though that would only be apparent to readers, not to the characters. He has a beautiful airship that the pair wind up flying, and a harpy-like woman to serve as their guide. He also gives them a pack of cards, which they think is silly. Sadly, the airship doesn't last that long, getting shot down, and the pair wind up in the rebels hands.
The harpy seems to desert Fafhrd and Mouser, but is really just going off to get water, with which she douses the cards, bringing them to life. Things seem to be going well, and the rebels get defeated, but then it turns out the princess didn't want to be rescued. She had been planning to marry the rebel leader.
Thee princess tries to kill Mouser, but the harpy gets in between, sacrificing her life to save him. Makes for a powerful ending, even if it is a downer.