Q-Space

From the book jacket:

The unpredictable cosmic entity known only as Q has plagued Captain Jean-Luc Picard and the crew of the Starship Enterprise 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 the crew needs is a visit from an omnipotent troublemaker so, naturally, Q appears.

Q has more in mind than his usual pranks, and while the Enterprise struggles to defeat a powerful inhuman foe, Picard must embark on a fantastic odyssey into the Q Continuum itself, with the fate of the galaxy hanging in the balance.