The Gates of Terra is a short story by Nick Kyme in the Horus Heresy series. It was first published in the 2012 Games Day Chapbook (France).
As the Heresy spreads across the galaxy and confusion reigns, only one thing is certain: Horus and his traitor Legions will eventually strike at Terra. But he will not find it unguarded - the Ardent Reef, an encircling ring of gun bastions and asteroid bases, is but one amongst many such lines of defence. Captain Arcadese of the Ultramarines finds himself in command of a host of his battle-brothers, as the renegade Warmaster's fleet launches its final assault on the Throneworld. Will he hold the line even in the face of almost certain death, or will his own loyalty waver in those final moments?