Gates of the Devourer

No constructs of man are more terrifying than the God-machines of the Adeptus Mechanicus. Where these mighty mechanical behemoths walk, worlds tremble – few enemies can withstand the firepower of a Warlord Titan. The Imperial plan to save the world of Khania from a tyranid invasion looks the Navy will destroy the hive ships, and the Legios will take a supporting role on the planet itself. But when the transports of the Adeptus Titanicus arrive, they find the Navy fleet has been annihilated, and they must take on the full brunt of the tyranid ground force, no matter the cost.

Read it because
We're used to seeing the Titan Legions supporting a larger Imperial army, but what do they do when they're alone, outnumbered, surrounded by xenos monstrosities?