[b]Season 1:[/b]
Episode 1: “Pilot” - We are introduced to the characters and themes of the show.
Episode 2: “The New Girl” - Lanie Lancaster arrives on the scene.
Episode 3: “Incident at Terry’s Diner”
Episode 4: “Francis Callahan is a Gay Man” - Francis comes out as gay (This episode won an Emmy).
Episode 5: “Halloween”
Episode 6: “Mike Averstin and the Philosophers Stone”
Episode 7: “Hard Girls”
Episode 8: “All the Best Cheerleaders Have Daddy Issues” - Winona Davies dies from a drug overdose.
Episode 9: “Loss” - The cast struggle to cope with the loss of Winona.
Episode 10: “Oh Captain, My Captain” - In a afternoon detention, Mr Beau tries to inspire his students.
Episode 11: "Lord of the Ridge"
Episode 12: "Graduation" - The older kids graduate and the focus of the show shifts to the younger generation.

[b]Season 2:[/b]
Episode 1: “Kids of Summer”
Episode 2: “Sid and Nancy” - An episode dedicated to the toxic relationship of Decky and Lanie.
Episode 3: “The People vs Logan Rivers”
Episode 4: “Mr Beau” - Mr Beau's mysterious past is revealed.
Episode 5: “A Game of Pool” - Beau's job hangs in the balance and is decided in a game of pool with principal pain.
Episode 6: “Catch Me, If You Can”
Episode 7: “The Election” - Louis runs for class president.
Episode 8: “The Dream Episode” - We learn what could have been as in this episode we see what Edenridge would have been like had things been just a little different.
Episode 9: “Carry on my Wayward Son”
Episode 10: “What Would You Say?”
Episode 11: "The Last Picture Show"
Episode 12: "Calling all Celtics"
Episode 13: "Sundance Part 1" - Principal Payne takes the gang to Sundance for some fun in the snow.
Episode 14: "Sundance Part 2" - Secrets and lies are revealed and things will never be the same again.

[b]Season 3:[/b]
Episode 1: “Broken Kids of Boston” - The fallout from Sundance continues far beyond summer.
Episode 2: “Charlie’s Got a Gun”
Episode 3: “Walk the Line”
Episode 4: “Roddy vs the World”
Episode 5: “Rage” - A student brings a gun to school and chaos ensues
Episode 6: “What Is Left of Them?” - The aftermath of the school shooting is revealed (Episodes 5&6 were shown back to back and are considered one long episode by most, it won an Emmy)
Episode 7: “Brothers and Sisters”
Episode 8: “Come Together”
Episode 9: “Prom” - Its Prom night in Edenridge.
Episode 10: “The Hard Goodbye” - The kids graduate and the next generation walk into Edenridge High

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I'll fill in plot details as we go for every episode I think.