Prue sits forlornly by a dock extending to a lake at a summer camp named Camp Skylark. A black-and-white flashback shows her mother being zipped into a body bag as young Prue calls for her. In the present, Piper calls and Prue says she is stuck in traffic. Out on the lake, a park ranger sits in a boat as the water churns near him. Suddenly, something pulls the man into the water. Prue runs toward him, but a strange old man stops her.
Piper is planning to have breakfast tomorrow with Dan. Prue comes home and says she saw someone drown at the lake. Piper and Phoebe are upset at the lie, but Prue convinces them to come to the lake with them, for the camp is to be reopened. They will look for the strange man and for Mrs. Johnson, who ran the camp and still lives in the same cabin.
Prue goes to her office and finds Jack sitting in her chair. He is his usual carefree self, especially since he has finally decided to accept a job at Buckland's. Prue decides to leave him there while she deals with the camp.
Piper and Phoebe meet with Mrs. Johnson. She had planned to reopen the camp until that day's drowning. The sisters inquire about the strange man, and they leave her cabin and meet with Prue by the lake. His name turns out to be Sam.
Jack calls Prue and announces that he is taking her lunch with a client, Mr. Fujimoto.
As the sisters look for Sam, Mrs. Johnson tears down the "Welcome Campers" sign. She sees the water churning by the dock and goes to investigate. Suddenly, the ranger leaps out of the water and pulls her in.
The sisters find the shed where Sam lives, and Prue finds a picture of their mother. Piper finds a certificate naming "Sam Wilder" as "Teacher of the Year" -- in 1872. Leo suddenly orbs in and urges the sisters to leave before Sam returns. He says that Sam was their mother's Whitelighter. Sam clipped his wings after their mother died.
After Leo orbs away, the sisters see Mrs. Johnson--or so it appears--thrashing about in the water. The sisters run to her, but Sam urges them to get off the dock. He tells them that a Water Demon lives in the lake, and one of the ways it kills is by possessing its dead victims' corpses and making other people think they're drowning. He doesn't think the sisters are strong enough to fight the demon because their mother couldn't fight it either. They insist, and finally Sam blows some dust in their faces, and sends them home to sleep.
The next morning, the sisters don't feel so well and Piper's arms and legs are covered with poison ivy. Dan appears with breakfast; the two were due to have a date that morning. However, Piper can't remember Dan ever asking. Dan sees her rash and backs off. Leo orbs in, and Piper freezes Dan to talk to him. The sisters can't remember much of anything about the past day, but Leo tells them again of the lake, the demon and Sam. The powder wears off, allowing the sisters to jog their memory. Piper unfreezes Dan and tells him she's unwell and doesn't feel up to a date. Phoebe and Prue head to the lake and send Piper to bed.
Prue and Phoebe arrive at the camp and find it full of children. Prue confronts Sam about his using the dust, as well as for not protecting her mother. Sam says he clipped his wings because he felt like he couldn't do any more good, but Prue convinces him to help them vanquish the water demon. She asks for some of the powder, and he gives her a packet.
Piper wonders why Leo can't heal her, but Leo tells her he can only use that power when he's meant to. Leo flips through the Book of Shadows, but finds nothing on the water demon. Piper finds a stack of love letters in the laundry basket, written by her mother to Sam.
Phoebe stalls the children, who insist on going swimming. Prue arrives, and in that moment Jack calls. He conferences with Mr. Fujimoto, who asks Prue about a carousel horse. She wings it, but Jack cuts in, speaks a bit of Japanese, and closes the sale. When the call ends, Phoebe blows the dust on the children and sends them to bed.
Piper and Leo read some of the love letters, which tell of how hard it is for a witch to love a Whitelighter. Piper and Leo can relate. At last, they decide to join the others at the lake, and Leo orbs with Piper. Leo says that Sam was in love with Patty. Sam blames himself for her death. Phoebe takes Sam's hands to find out how her mother died.
In a black-and-white flashback, Patty takes a pair of jumper cables as the demon rises up behind her. Sam yells "Look out!" Patty turns and drops the cables to freeze him. The demon is immune to Patty's freezing power, and drowns her from the inside.
The sisters try their mother's plan again, but this time Prue with telekinesis, rather than Piper (or Patty) with freezing, will confront the demon. Prue takes the cables while Sam stands ready at the switch. The water churns behind Prue, and Piper tries to warn her. Leo runs after Piper, and history repeats as Piper turns and freezes him. Sam confronts the demon, barring it from taking Prue, and the demon enters Sam. Sam regains control of himself and grabs the cables; Prue remotely flips the switch, electrocuting the demon, but mortally wounding Sam. Leo unfreezes, and the sisters urge him to heal Sam. However, he can't; apparently it's Sam's time to go. Sam doesn't mind, he says he'll be able to see Patty again. Patty's ghost appears as Sam dies, and his ghost appears at her side.
Prue confronts Jack in her office. He has listed her as the sales agent, to her surprise. She offers him dinner.
Phoebe adds the letters to a photo album. Leo orbs in and pulls Piper aside. Both are conflicted. Leo isn't leaving, but feels he can't be the sisters' Whitelighter because he can't stop loving Piper. Leo orbs away, and then Dan knocks at the back door bearing breakfast.