Hard science sf, involving other worlds, weird machines, computers and assorted bad guys; real-life physicist Cramer's debut. Physics experimenter David Harrington and his stunning, brainy assistant Vickie Gordon accidentally stumble on the "twistor" effect: pieces of earth real-estate vanish and are replaced by chunks of other-worldly shadow matter (this, imperceptibly, occupies the same space as our own world, but in various different dimensions). Thus, David and Vickie discover several new worlds, at least one of them habitable. However, David's superior, Allan Saxon--already committed to various illicit deals involving stolen computer components--finds out about the twistor effect, and immediately sees profitable implications. Unfortunately, Saxon's criminal co-conspirator Martin Pierce also finds out, and eventually dispatches thugs to steal David's device. But, in the ensuing struggle, David and two children are "twisted" into a habitable shadow world. Here, as the kids explore their strange new surroundings, David experiments desperately, trying to find a way to return home; meanwhile, the bad guys torture Saxon for details, then kidnap Vickie with dire threats. Decidedly uneven work, ranging from the often scintillating hard science to banal evildoers and uncontrolled plot (better to eliminate the bad guys altogether). A promising debut: good on science and scientists, but cluttered with improbable melodrama.