Take a demon, whose job is to watch over the people in Hell who feel
guilty, and agree with them every time they say they've done something
bad, and imagine him leaving his post and taking a vacation. It's
breaking a bunch of rules, but what's the worst that can happen?
He decides to possess the body of a sullen teenage boy, and find out
about being corporeal, and investigate sin (including that one called
lust). The story is hilarious and charming. The demon goes into
paroxysms of joy when he gets to experience such things as sneezing.
Considering that everything looks new and fabulous to him, he can't
sustain the sullen teenager act for very long.
He also discovers that he can actually affect people, as opposed to in
his old job where he felt completely useless. He thus starts up a
bunch of "projects," matchmaking and dissuading someone he sees as a
potential future client.
It's short, it's funny, it has a nice little discussion of angels and
demons. Go read.