The 3rd Legion is in ruins. Almost wiped out after an assault went horribly wrong, their survival teeters on the brink of disaster.

Not only that, their commanding officer doesn't quite seem to be himself.

A side story in the Legends of Equestria timeline. Reading the other stories in the series is recommended, but at a bare minimum you must have read The Legionary in order to understand what is going on; https://www.fimfiction.net/story/469881/legends-of-equestria-the-legionary