Out of Time — Mike Stone

"Out of Time" is the fourth science fiction novel in the Rational Series. It takes off sometime after the end of "The Rats and the Saps" where Sapiens are at peace with Rationals and vacationing on each others' worlds. Tourism is complicated by the fact that Sapiens come from a 3-dimensional world and the Rational world is 11-dimensional. After nearly getting himself killed while trying to walk in a Rational park, Cadmus is rescued by a Rational couple, Remi and Galen, and nursed back to health. After Cadmus returns home to his world, Galen visits Cadmus with an urgent request to stop a vastly superior species, called the Frats (Future Rationals) from dismantling our Universe, hypercube by hypercube. Cadmus agrees to come along, although he doesn't see what he could possibly do to help, as long as he can bring along his trusty dagu, Lonesome.