The Horus Heresy: Betrayal at Calth

From the official description:

"The Horus Heresy: Betrayal At Calth is a fantastic standalone boxed game of claustrophobic tunnel combat, set during the Word Bearers’ invasion of the Ultramarine world of Calth. Emphasising fast-paced squad-based combat during six exciting missions, it allows players to choose their side and command a force of beautifully detailed Citadel miniatures in a brutal war for survival, during one of the iconic battles of the Horus Heresy."