It's the most unusual medical unit in the galaxy – and it makes house calls. A fully equipped starship lab, Taylor's Ark is run by Dr. Shona Taylor, a specialist in environmental medicine. She has a menagerie of very special assistants, including an Abyssinian cat, a dog, rabbits, mice, and an alien ottle named Chirwl.

Now, this highly trained crew faces the ultimate medical mystery. On Chirwl's home world, humans and ottles alike are aging at an alarming rate. And if Dr. Taylor doesn't find a fast cure, the entire colony will die ... of old age.