Twilight promises Rarity that a new, experimental spell will make her stronger, smarter, and faster. It works! Yet Rarity wakes up the next morning only to discover a strange side effect. She looks in the mirror and sees a... he. Twilight sheepishly suggests that Rarity enjoy this "vacation from herself" and wait until the spell undoes itself, a full week later.

He calls this new male self 'Purity', and he pretends to be Rarity's cousin, helping out after Rarity left for a sudden business trip. Purity tries to keep things quiet, and he goes about life as normally as possible. However, a new body means new... urges. Purity struggles to keep himself off of his old friends. He also must deal with a new customer named Blackberry, just coming in from Hoofington, that falls head-over-hooves in love with him. Blackberry feels rather weirded out, since he's only been into mares before, but Purity seems just so elegant as well as so incredibly beautiful. Purity can't seem to help himself from falling into the same trap.

Can Purity keep his relationship with his friends from turning into something pervy? Can Purity tell Blackberry the truth? What will happen when the seven days run up?