Mara, Tamblyn circle '127 Hours'

Kate Mara and Amger Tamblyn are joining Danny Boyle's Slumdog Millionaire follow-up 127 Hours.

The pair will appear opposite James Franco, who was last month cast as Aron Ralston, a mountaineer who gets trapped under a boulder in Utah and is forced to cut off his own arm in order to set himself free.

Mara and Tamblyn will play hikers who encounter Ralston before his accident, says The Hollywood Reporter.

Boyle is reuniting with his Slumdog writer Simon Beaufoy on the true-life story 127 Hours, which will begin filming next month and could debut in cinemas before the end of the year.