Trial of Fire

The event known as the Trial of Fire was a campaign conducted by the Invictors of Mars Space Marine Chapter to assist an unnamed, besieged Imperial world from the Forces of Chaos. When the Chapter began their assault, they were immediately set upon by hordes of daemons, which threatened to annihilate the attacking Astartes. The Invictors suffered near-catastrophic losses, with only three companies escaped the slaughter, as well as the loss of all the Chapter's librarians and chaplains.

History
The Invictors of Mars received a vox signal which they would follow for several years until they found the world from which the signal originated. Upon landing, waves of daemons came running to rip and tear the Astartes. When they were to try and escape to the ships shackles of fire grabbed their greaves and hands unable to retaliate they were mercilessly slaughtered. Only 3 companies escaping after all librarians and chaplains died. It is unknown how they escaped but it was called by the chapter as a miracle made by the Emperor of Mankind.