A Tyranid hive fleet has been discovered dangerously close to the solar system. Two full companies of Ultramarines, led by the legendary Chaplain Cassius, were sent to destroy the aliens. They must stop their enemies at any cost. The Ultramarines perform their duty with characteristic courage, bravery and honor. But the enemy turns out to be much stronger than they expected, and because of Cassius’ impulsive nature, disagreements that are unacceptable in such a situation flare up in the ranks of the Space Marines. Now the success of the operation hangs by a thread.