Shattered Legions by Dan Abnett

Driven almost to the brink of self-destruction at Isstvan V, the Iron Hands now seek vengeance for the murder of their primarch Ferrus Manus. Gathering survivors from the Raven Guard and the Salamanders aboard any vessels capable of warp travel, these Shattered Legions wage a new campaign of annihilation against the traitor forces across the galaxy – a campaign masterminded by legendary warleader Shadrak Meduson.