From fox.com:
"ECHO (Dushku) is an "Active," a member of a highly illegal and underground group of individuals who have had their personalities wiped clean so they can be imprinted with any number of new personas. Hired by the wealthy, powerful and connected, the Actives don't just perform their hired roles, they wholly become -- with mind, personality and physiology -- whomever the client wants or needs them to be. Whether imprinted to be a lover, an assassin, a corporate negotiator or a best friend, the Actives know no other life than the specific engagements they are in at that time.

Confined between missions to a secret facility known as the "Dollhouse," Echo and the other Actives including SIERRA (Dichen Lachman), are assigned engagements by ADELLE DEWITT (Olivia Williams), one of the Dollhouse leaders. After each scenario, Echo, always under the watchful eye of her handler, BOYD LANGTON (Harry Lennix), returns to the mysterious Dollhouse where her thoughts, feelings, experiences and knowledge are erased by TOPHER BRINK (Fran Kranz), the Dollhouse's genius programmer.

Echo acts with no memory of before. Or does she?

As the series progresses, FBI Agent PAUL BALLARD (Tahmoh Penikett) pieces together clues with the help of Russian informant, LUBOV (Enver Gjokaj), that lead him closer to the Dollhouse. Echo stops forgetting as her memories begin to return, and she slowly pieces together her mysterious past."

Echo assumes the role as a negotiator for a kidnapping while a new girl joins the Dollhouse.

Echo is hired to go on a date with a man who likes to hunt bigger game than the wildlife.

Echo and Sierra go undercover to protect a pop star who is being stalked by a fan.

Echo loses her memories in the middle of a high-tech heist to retrieve stolen art.

Echo goes undercover as a blind woman to infiltrate a heavily guarded cult.

Paul's interest in the Dollhouse becomes obsessive as he begins a relationship with Mellie. When Echo is sent to assasinate him, she ends up in a catatonic state.

Echo investigates a university that she recognizes while Topher and Adelle have fun after being infected with a mind altering drug.

Echo, Victor, Sierra, and November regain their memories and escape the Dollhouse.

Topher tells Adelle that there is a spy and the operatives are programed to find out who is the mole.

Echo is programmed with Adele's dead friend's memories in order to find out the truth about her death.

Echo helps a young girl deal with her past while Sierra goes undercover as an FBI agent to investigate a corpse found in Arizona that is believed to have been killed by Alpha.

Alpha uses Echo to kidnap a girl. Meanwhile, Ballard assists the Dollhouse in tracking down Alpha and Dr. Saunders discovers she is actually an active.

Echo infiltrates the home of an arms dealer by marrying him. After finding out that she is a doll, Claire is not sure if she wants to give her body back to her original personality. Paul puts his life in danger in an attempt to make things right.

Topher explains to Paul that he has figured out a way to program the mind in a way that affects the body. Paul sees this development in action during Echo's new mission.

Victor is impanted with a psychopath's mind in order to locate kidnapped women. Meanwhile, Echo flirts with a college professor.

Sierra confronts the man who put her in the Dollhouse. Meanwhile, Boyd learns that Echo is capable of remembering her experiences as an active.

Senator Perrin is kidnapped by Echo before testifying about the Dollhouse. Topher and Adele team up with the D.C. branch to recover rogue actives.