The Sackers. In all Captain James T. Kirk's travels, he has never found a race more universally shunned and abhorred. Their mere appearance causes most Federation members to become violently ill.

Now the Sackers have performed a deed whose brutality matches their horrifying exterior. They have stolen a revolutionary new scientific device - murdering an entire race in the process - and used it to create a rip in the fabric of space, a hole through which another universe is rapidly leaking. Unless Captain Kirk and the crew of the Enterprise can find a way to stop the new universe's expansion, it will consume - and utterly destroy - our own.