various
Shattered Legions
part 43

After the massacre at Isstvan V, the broken remnants of three Legions formed a guerrilla force dedicated to slowing Horus's advance on Terra. The ten tales in this volume relate exceptional stories of heroism by these Shattered Legions.
The Horus Heresy
anthology

It contains:
The Keys of Hel
Grey Talon
The Hand Elect
Immortal Duty
The Either
Deeds Endure
Unforged
Meduson
The Seventh Serpent
Unspoken
The Noose

Also in:
Books 41-43: Unabridged Audiobook Collection