Tess Gerritsen used to be a doctor, so it comes as no great surprise that the medical parts of her latest thriller are very convincing, even if most of the action happens in a place where few doctors have ever practised--outer space. Dr. Emma Watson and five other hand-picked astronauts are about to take part in the trip of a lifetime--studying living creatures in space. But an alien life form, found in the deepest crevices of the ocean floor is accidentally brought aboard the shuttle Atlantis. This mutated alien life form makes the creatures in Aliens look like backyard pets. Soon the crew are suffering severe stomach pains, violent convulsions and eyes so bloodshot that a gallon of Optrex wouldn't help. Gerritsen brilliantly describes the difficulties of treating sick people inside a space module, and how the lack of gravity affects the process of taking blood and inserting a nasal tube. Dr. Watson does her best, but her colleagues die off one by one and the people at NASA don't want to risk bringing the platform back to Earth. Only Emma's husband, a doctor/astronaut, refuses to give up on her. As we read along, eyes popping out of their sockets, all that's missing is one of those bland NASA voices saying, "Houston, we have a problem--we're being attacked by tiny little creatures that are part human, part frog and part mouse." Here are some other examples of Gerritsen's controlled medical horrors:Bloodstream, Harvest, and Life Support. --Dick Adler