Star Trek: The Next Generation: The Dominion War, Book 1: Behind Enemy Lines

From the Gamma quadrant they came -- hordes of fierce Jem'Hadar warriors commanded by the mysterious Changelings, who will stop at nothing to achieve victory over both the United Federation of Planets and the Klingon™ Empire. Now that the Dominion has entered into an unholy alliance with the Cardassian military regime and seized control of Deep Space Nine™, Starfleet finds itself fighting a losing war against unbeatable odds. As mighty fleets clash in the deadly battleground of space, the fate of the entire Alpha Quadrant hangs in the balance.
The Enterprise-E is patrolling the Cardassian border, bracing for the joint Dominion-Cardassian offensive that Starfleet knows will come soon, when Captain Jean-Luc Picard and his crew are reunited with a former crewmate, friend, and enemy: Ro Laren. The onetime officer, who defected from Starfleet to join the rebel Maquis, brings disturbing news. Deep behind enemy lines, the Dominion is attempting to build an artificial wormhole that will allow them to bypass the mined Bajoran wormhole and bring fresh reinforcements into the Alpha Quadrant, altering the balance of power irrevocably. If Captain Picard cannot stop the project, the new wormhole will guarantee the ultimate victory of the Dominion!