An artifact is disovered in the ocean - and appears to not be human as many tests fail to penetrate it.
An outside expert is brought in to help on the research into it.
After this, there are three strands to this book - the research in to the artificat, and the history of two long-lived alien shapeshifters on the planet, both to converge in the present time at the artifact site.
One of them is a martial killer, able to take the form or any man, and has been in armies since the stone age.
The other remembers back to the thirties and also living in the ocean, as whales, sharks, etc., where it became a boy, and then took a variety of forms after that, often female.
3 out of 5