Action and Consequence

Synopsis

Newly promoted to leader of his squad, Silver Skull Gileas Ur'ten must prove himself both to his battle-brothers and his peers. When a mission to protect their recruiting grounds against the dark eldar goes wrong, Gileas must lead a force to locate the missing Space Marines, and go to their aid. However, the need to protect the eldar's human prisoners poses extra complications on an already tricky mission.

Read it because Space Marines are at their best when they can unleash their whole strength upon their enemy... so when the situation requires that they hold back lest innocents get hurt, things get complicated... especially when they're fighting dark eldar, who are only too happy to put their captives in harm's way.