I ran a short plot that works well for low level characters, say below 3rd level, went like this:
A bard or minstrel PC wanted to purchase a new musical instrument. When he gets to a shop, he looks them over and sees a really nice one in the back of the shop made by a well known instrument maker. He asks the shop keeper how much and the shop keeper asks for a price, which isn't very high for one of such quality, especially one made by an instrument maker of such repute. Anyway, the shop keeper really wants to sell the instrument, and at any price (should play this out so the player gets that hint but it isn't too obvious), for his own peace of mind.
After the player gets the instrument and gets it home, he should be happy. Then after a few days (you might want to make this after some intervening adventure to not make things too obvious to the player), he starts having bad dreams. He dreams of a fat man with a knife in hand who is laughing down at him, as he experiences the vertigo of falling. Of course, he never hits the ground but always wakes up before he hits the ground. You'll want to start these dreams off murky, but elaborate on them as you go. You might also have another PC wake up one night to see the PC playing the instrument (let's say a mandolin) and singing in a totally different voice. When the player wakes up, he remembers nothing. Then one day, the other characters in the party will find the PC is missing. They should find him walking down the road, singing in that foreign voice.
The mandolin is the focal point for a ghost, not really a malevolent ghost but one that wants revenge and restitution from the burghermeister of a nearby town. The ghost was once a chaotic good bard who liked to poke public fun at corrupt people and who was a little too free with women, especially married women. He died when fleeing from the bedchamber of the irate and corrupt burghermeister, who caught him with the burghermeister's wife. Now his death was really an accident since the burghermeister did not knife him, and the bard fell from the window and broke his neck. But the ghost wants to humiliate him nevertheless and drive him from his comfortable office. He isn't interested in killing the burghermeister, just wants to show him up for what he is, a corrupt and petty man. That's why he "borrows" or possesses the body of the owner of the mandolin to lead him to the town to exact his revenge on the burghermeister. Hopefully, the other PCs of the adventuring group would be drawn in to this effort.
Since the ghost is not evil, a detect evil would not show the mandolin as evil. Destroying the mandolin would destroy the link with the ghost, but any attempts to do so would make the ghost extremely angry.