While Serena and Luna are watching a live action performance of Sailor Moon (Molly and Melvin are also in the audience), a Cardian named Four Face appears to steal energy from the audience. Four Face gives the energy to the Doom Tree, which doesn't respond, so Alan and Ann skip school the next day. Serena, Amy, and Lita notice that they are missing and go to check and see if they are all right.
Alan invites them in but Ann is rude to them and yells at them to leave. Serena later returns and tries to enter Alan's room, but the Doom Tree attacks her with its vines. Alan says that it is part of his science class. Once she is gone, Alan and Ann decide that the Doom Tree must love Serena's energy.
Lita notices a piece of the Doom Tree in Serena's hair. Luna and Artemis examine it and get the same energy from it as from Cardians, and they decide that Alan and Ann must be from the Negaverse.
Serena goes to Alan and Ann's apartment, and runs into Darien, who has flowers for Ann. Ann takes Serena into the room with the Doom Tree. Four Face takes Serena's energy, and the Doom Tree grows to massive proportions and traps Serena and Four Face in its vines, killing Four Face. The other Sailor Scouts transform and try to enter the apartment.
- First and last appearance of Cardian Four Face
- Alan and Ann's true identities are revealed to the Sailor Scouts
- The title of the episode is based on the title of a book called The Secret Garden