The novel was first published in hardcover by William Morrow in 1989, then in mass market paperback by Avon Books in 1991.
After industrial espionage causes problems, physicist David Harrison finds himself lost with two small children in an alternate universe where the six-legged wildlife is dangerous and aggressive.
David has to find a way back home, while dealing with the spies that caused the problems in the first place.
In 1967 Roger Penrose developed a general relativity approach called Twistor theory to apply to the study of quantum gravity.
[1] Publishers Weekly called the central situation appealing, but the reviewer noted, "Given Cramer's dry, stiff, academic prose and the equally dry, stiff, academic characters, the interesting and dramatic kernel of physics speculation will open only to the most persistent of readers.