Where there is smoke there is fire

Remus and Sirius have peacefully been flatmates since finishing school, both going about their life's occasionally meeting their friends and throwing parties, really everything was just as it should be.

That is until one day Remus walks into the kitchen to get his usual cuppa to be met with a half naked girl wearing Sirius' shirt and having hickeys plastered along her neck and collarbone.

After that Remus starts to question some things and complicated chaos ensues.