A character is participating in events they have no memory of. They catch on to it slowly, because it's mostly innocuous day to day stuff, but eventually the evidence is piling up and impossible to ignore — "they" are doing things on a fairly regular basis that they are not actually doing!

The culprit? A wife/sister/friend has been using polyjuice to masquerade as them. Maybe they're trying to cope with gender identity struggles. Maybe they're a feminist who needs to occasionally be a man to just get shit done. Whatever their reasons, this polyjuice situation has to stop... before things get complicated.