Star Trek: The Dominion War, book 03 : Tunnel Through the Stars
John Vornholt1998

From the Gamma Quadrant they came, hordes of merciless Jem'Hadar soldiers commanded by the shape-changing Founders, who seek to conquer both the United Federation of Planets and the Klingon Empire. Now that the Dominion has joined forces with the Cardassians, and claimed Deep Space Nine as their prize, Starfleet is running out of time. As a secret military project nears completion, the destiny of the entire Alpha Quadrant depends on the courage of a few.

In the Federation's time of greatest peril, as the Enterprise readies itself for battle, Captain Jean-Luc Picard leads a desperate mission of espionage deep into the heart of the hostile Cardassian Empire. Unless they can prevent the Dominion from creating an artificial wormhole, hordes of fresh Jem'Hadar warriors and Changelings will pour into the Alpha Quadrant, dooming the Federation to unconditional surrender. But there may be a traitor along on the mission and Picard finds he cannot trust even his closest allies.