War of Fire and Shadow
Deep in the 37th Millennium the Emperors Dragons were left reeling after a brutal and costly war against Hive Fleet Medusa. The Tyranid advance had been halted and eventually destroyed by the might of the Dragon Legion but the casualties had been incredible. Almost a quarter of the legion had lost their lives in the defence of the Imperium. Even with the pre-emptive, demi godlike power of a Primarch spearheading the defence, the cost of lives had been inevitable and the entirety of the Imperial forces would have likely been lost altogether had none other than a primarch led them.
