Deathwatch Series by C.S. Goto

First in a series of Deathwatch titles. When the Deathwatch Space Marines are sent to investigate a vital outpost on a lonely planet, they find they have been betrayed. Can they escape the ravening hordes of giant bug like monsters called Tyranids and find the traitor who lurks in the heart of the Imperial forces?

Second novel of the series. When an ancient pact is invoked, the Deathwatch Space Marines must put aside their prejudices to battle alongside the alien eldar to protect the galaxy from an even greater menace.