The Wounded Sky
Star Trek (Pocket Books) #13
"An alien scientist invents the intergalactic inversion drive, an engine system that transcends warp drive – and the USS Enterprise will be the first to test it! The Klingons attempt to thwart the test, but a greater danger looms when strange symptoms surface among the crew – and time becomes meaningless.
Now Captain Kirk and his friends face their greatest challenge – to repair the fabric of the universe before time is lost forever."