Keira Knightley has signed on to join Andrew Garfield and Carey Mulligan in Fox Searchlight's upcoming sci-fi thriller "Never Let Me Go."

According to Variety, the plot centers on three people who grew up in isolation in a boarding school and discover they are clones created only for the purpose of organ donation.

Mark Romanek, whose credits include "One Hour Photo," will direct a script by Alex Garland ("Sunshine").

The trade said the film will head into principal photography in April.

Knightley was last seen in "The Duchess." She has plenty of projetcs coming up, including "Last Night," "London Boulevard" and "King Lear."

Garfield's credits include "Lions for Lambs" and "The Other Boleyn Girl." Mulligan will soon be seen in "Public Enemies" and "Brothers."