Sirius feels just like Fred and George using Extendable Ears to listen in on the Order meetings. Even worse, he sits in on the meetings and gives opinions but he can't do anything. Everyone expects him to explode in frustration at any moment. Except Remus. He has been on the receiving end of caution and fearful sympathy before and knows it's hollow. So he fills Sirius up with action. They toss plans back and forth, mulling them over with fierce determination. They are part of something. No longer Marauders but Order members. And Remus is worth fighting for, dying for.