The Q Continuum: Book One: Q-Space (Star Trek: The Next Generation 47)

The unpredictable cosmic entity known only as Q has plagued Captain Jean-Luc Picard and the crew of the Starship Enterpriseâ„¢ since their very first voyage together. But little is known of Q's mysterious past or that of the unearthly realm from which he hails. Now Picard must learn Q's secrets -- or all of reality may perish!
Ever since its discovery, the great galactic barrier has impeded humanity's exploration of the universe beyond the Milky Way. Now a brilliant Federation scientist may have found a way to breach the barrier, and the Enterprise is going to put it to the test. The last thing Picard needs is a return visit from an omnipotent troublemaker so, naturally, Q appears.
But Q has more in mind than his usual pranks, and while the Enterprise struggles to defeat a powerful inhuman foe, Captain Picard must embark on a fantastic odyssey into the history of the Q Continuum itself, with the fate of the galaxy hanging in the balance.