Isla Fisher is writing a thriller with her mum.

'The Great Gatsby' star has admitted if she hadn't become an actress, she would have become a full time writer and after mastering the art of performing, she's now ready to try her luck at a screenplay.

The 37-year-old star has teamed up with her mother, Elspeth Reid - who helped her publish two teen novels, 'Bewitched' and 'Seduced by Fame' when she was 18 years old - to create a film, which she claims has been challenging, but amusing.

Speaking in an interview with Britain's Cosmopolitan magazine, Isla said: ''My mum and I have actually been writing a script for a thriller together. It's really fun. She doesn't understand the rules of screenwriting, so I'm often like, 'What?! Mum, you can't kill off the protagonist on page 10!' She breaks all the rules, which makes it original at least. We've had a scream doing it.''

Australian Isla - who is married to Sacha Baron Cohen - may have made it in Hollywood, but admits it has been a hard journey, with her first agent in the US firing her.

She added: ''I really have had no help. In fact, the one time I did ask for help was after my agent in Los Angeles fired me. I was auditioning for all sorts of things but kept getting told 'no', so she just fired me!''