Ça fait mal

After war Remus Lupin got a job at the Ministry where he met the perfect boy, an auror Sirius Black. Despise the mutual attraction they hate each other and yet Dumbledore for some reasons decided to send the two of them on a mission and neither of them can really refuse. The mission is serious, the war is over but there are some things that have to be dealt with - not only the dark magic.