The Three-Minute Universe by Barbara Paul

The Sackers may be the most hated race in the galaxy, so repugnant that their mere appearance makes most Federation citizens ill. That hatred runs both ways, and now the Sackers have stolen a powerful new device that they use to imperil the rest of the universe. They've torn a hole in the fabric of spacetime, an expanding tear so that one universe is leaking into another, and unless the Enterprise crew can stop it, it will consume everything in its path.

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