The Rook by Daniel O'Malley.
Here is the description from Amazon:
"The body you are wearing used to be mine." So begins the letter Myfanwy
Thomas is holding when she awakes in a London park surrounded by bodies
all wearing latex gloves. With no recollection of who she is, Myfanwy
must follow the instructions her former self left behind to discover her
identity and track down the agents who want to destroy her.
soon learns that she is a Rook, a high-ranking member of a secret
organization called the Chequy that battles the many supernatural forces
at work in Britain. She also discovers that she possesses a rare,
potentially deadly supernatural ability of her own.
In her quest
to uncover which member of the Chequy betrayed her and why, Myfanwy
encounters a person with four bodies, an aristocratic woman who can
enter her dreams, a secret training facility where children are
transformed into deadly fighters, and a conspiracy more vast than she
ever could have imagined.
This was an easy fast read. A good one to read at the beach. Amnesia stories are usually not my favorite. This book took a new angle. Plus it's totally whacked.