Remus is on the verge of doing a happy dance right here in the hallway in front of the three students. He settles for stunning the rat. (The very, definitely, familiar, toe-missing rat.)
Now he just needs to get back to the others before anyone – particularly a certain stalking, gloomy dungeon bat – finds him and holds him up even further. For all he knows Tonks has already contacted Moody and Sirius is right now being arrested.
….and too late.
"Well, well, well Lupin. You've caused quite the stir. Apparently people have finally cottoned on to your disappearing act."
Remus turns to face him and gives him the most genuine smile he can muster. "I didn't mean to concern you Severus."
Snape recoils with such a look of disgust that Remus has to double check his mental calendar to make sure tonight isn't the full moon and he hasn't let a little bit of Moony slip through.
"Professor Lupin." Hermione pipes up before he can flee. "What are you doing with Ron's rat?"
All eyes fall on Peter. Remus struggles to come up with a good excuse. "This rat is wanted in a criminal investigation."
Remus had never been a great liar. He was probably only a few seconds from bringing up his dying grandmother.
"Criminal…" Snape drawls, clearly making an unsubstantiated – and sadly not inaccurate – guess. "Has your old friend come to kill you Lupin? You're looking remarkably unscathed for someone who's had a run-in with a murderer."
Remus is almost certain that Professor Dumbledore had made Snape promise not to insinuate these things around the students. Obviously he had forgotten the clear loophole of Snape flat out telling people his theories.
"I have to go." He replies weakly, hands tightening on the unconscious rodent.
"Go where Lupin?" Snape drawls. "Why, you haven't even contacted the dementors."
Remus feels his face go white; unable to bear the thought of it he turns and runs down the hallway, towards his office and the closest floo.