Echo is an active in the Dollhouse. Her name before activation was Caroline.
Caroline became a type of peaceful but slightly radical activist after leaving college. She had become obsessed with Rossum Corporation, a very large pharmacy firm, who is doing animal drug testing at a lab located at a nearby college. She enlists the aid of her boyfriend to break into the lab and video tape what they are doing inside. Once inside they discovered there are doing more than animal testing, but experimenting with human fetuses. They are caught by security guards, flee, and in the process her boyfriend is shot and she becomes entangled with Adelle, the head of the local Dollhouse who makes Caroline an offer she can't refuse. Join them for five years and then get a clean slate and the rest of her life back or face the legal consequences of her criminal break-in.
Once inducted as a Doll (their insider names are military monikers, Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Sierra, Victor, etc.) her old identity and persona is wiped by an electronic process and they are given a base persona that is somewhat child-like and innocent, a blank slate state called Tabula Rasa. They have no serious egos and no sex drives in this state of inactivity. When they are called upon to perform a service for a client they are given a new, artificially created persona that is often a composite of many different real people selected like a cook selects ingerdients to go into a recipe. As a routine Doll, Caroline has had to "play" negotiator, background singer, wife and lover as an active, just as all the other Dolls are called upon to play roles for their clients whims. In Caroline's case, however, someone is starting to tamper with her implanted personas without the knowledge of the Dollhouse staff.
The are several people trying to bring the Dollhouse down (indeed, Caroline would be one of them if she were still outside looking in) including a rogue Dollhouse active named Alpha who went postal one day in the hive and attacked everyone except Echo (Caroline). Caroline is also being used by either a mole inside of the Dollhouse or someone, like Alpha, who is capable of penetrating the Dollhouse from the outside. Echo's mind and body are being used to help bring the Dollhouse down and to help an FBI agent (Paul Ballard) destroy the Dollhouse.
Echo has also been glitching. Her mind is growing, thinking outside the box, while still apparently toeing the "company line." It is unexpected but interesting, to Adelle, her mentor, at least, but not to other high ranking people inside the Dollhouse, which is a Rossum Corporation funded entity. At least one of these people, who once tried to burn Echo while on assignment, wants her put "in the attic" which is a process used for unstable persons (dolls or others), whereby their mind is COMPLETELY wiped and their comatose bodies are placed in a storage area (the "attic"), on minimal life support.
Echo is now everyone's pawn, being moved about the board without her knowledge for things unknown, or is she? Is she becoming aware? Is she thinking independently or is she just another Doll; mindless and obedient to the whims of those in possession of her...
company.