Warhammer 40k - Deathwatch - Steve Parker

When they first came together, Talon Squad were a disparate group of Space Marines from various Chapters. Under the auspice of the Deathwatch, trained in an ironclad Watch Fortress, they become a kill-team. Alien hunters, experts in xenos extermination, their first mission under the mysterious Inquisitor Sigma is a deadly one. Of all the enemies the Deathwatch face, the genestealers are amongst the fiercest, the most invidious. Led by Brother-Librarian Karras, Talon Squad must penetrate the bowels of a genestealer lair and put the abominations to the flame or face the consequences of an entire planet's extinction.

(Not sure why the info for book title and author is listed differently, but yes, this is the novel written by Steve Parker. Sorry for any confusion.)