Camouflage

A million years prior to the dawn of Homo sapiens , two immortal, shapeshifting aliens roam the Earth with little memory of their origin or their purpose. Later in the year 2019, an artifact is discovered off the coast of Samoa, buried deep beneath the ocean floor. The mysterious find brings two alien beings—the “changeling” and the “chameleon”—together again, to ponder the meaning of the object and its relationship to each other. Both immortals try to seek each other out and use the artifact to find their origins, one harbouring good intentions while the other is extremely hostile.
Won the Nebula Award for Best Novel in 2005.