Double Game: The City of Shadows

The "Double Game" series of books uses a combat and inventory system familiar to many "fighting fantasy" style books. But this one allows two players to play simultaneously (each using a different book of the pair). The books use cross-reference tables to allow the players to interact with each other (cooperating or otherwise) at certain points. One player player plays Coreus, the Prince. The other plays the Bardik, the Thief.