Seven years ago, Bob Kinnaird, high school student, encountered Hunter, a green protoplasmic glob of an alien, and became his host. Hunter is a police detective chasing a criminal, and he and his quarry have both crashed on Earth and are stranded. Since the quarry's crime is callous disregard for his hosts and placing them in danger, tracking him down and stopping him on a planet full of suitable but wholly unaware hosts is even more important.
That problem was resolved, and now, a college graduate with an engineering degree, Bob is coming home to the Polynesian island he grew up on. He's got a job as well as his family waiting for him. Unfortunately, he's also, quite possibly, dying, due to the same friendly alien symbiont who for years has protected him from illness and injury. His immune system and his blood clotting ability and other systems are simply failing, and Hunter, a cop not a medical specialist, has no idea how to fix it. He needs to contact his own kind and get the right specialists on the job, or Bob will die.
This is a difficult problem, but relatively straight-forward--until strange and dangerous accidents start to happen. Or rather, not accidents. One of Bob's trunks of books and possessions being shipped home is tampered with at the dock. His bike is tampered with repeatedly to cause dangerous accidents. The tiny group of trusted friends helping him and Hunter search for the wrecked ships and the means to contact Hunter's people also have accidents.
And they're running out of time, as Bob grows weaker and weaker, and more and more of his body systems start to fail.
The characters in a Hal Clement novel are never deep or complex; they're likable. If really strong characterization is essential for you, no Clement novel is ever going to satisfy. But his characterization isn't bad, either; it's just not very complex. Likable, smart characters are what he does.
What Clement is really all about, and what makes his books a joy, is clever, interesting ideas well grounded in science, along with good plotting that moves the story along. This is a satisfying, enjoyable read, and definitely worth your time--although you'll start off a step up in understanding Bob and Hunter if you read Needle first.
I borrowed this book from a friend.