A Clash of Kings
The Antler Men plot betrayal against King Joffrey I Baratheon and intended to abet the fall of the city to Stannis Baratheon. They arm several hundred men and plan, once fighting between Joffrey's loyalists and Stannis's forces has begun, to seize the Old Gate and let the enemy into the city. Master armorer Salloreon is a member of the group.
A Storm of Swords
A Feast for Crows
Varys: It seems they believe that Lord Stannis must win, and wish to share his victory. They call themselves the Antler Men, after the crowned stag.
Tyrion: Someone should tell them that Stannis changed his sigil. Then they can be the Hot Hearts.