Cat House

When Piper and Leo see a marriage counselor to work out their marital problems, Piper casts a spell that lets them literally see the key moments of their past. However, the spell goes awry and Phoebe and Paige are sent back in time to relive Piper's memories. They encounter an evil warlock stuck with them who is trying to kill their old cat Kit. After the warlock kills her in the past, the future changes in an unknown manner, but Phoebe and Paige get Piper to revisit the memory so they can change things. They stop the warlock and kill him, saving Kit who they realize was their familiar and Piper reverses the spell, setting them free.