Note: This is a short story, published initially in the Hammer & Bolter magazine and now part of The Primarchs Black Library book.
The Dark Angels are my space marine army since I collect Warhammer 40,000, so having more background about their primarch is quite appealing.
This story depicts Lion El'Jonson, through two Horus Heresy events: A chaos attack to the primarch's warship and mediating between Iron Hands and Death Guard chapters on a conflict in a Dark Angels planet.
You get a sharper image of the attitude, character and intelligence of the primarch, and at the end, a better picture of what Lion knew about Caliban before returning to the home planet. Even what or how was his idea of helping to finish the war.
A nice lore information burst added to the Dark Angels background. Too bad it feels too short.