The actress plays Selina Kyle, aka Catwoman, in Christopher Nolan's next installment of the franchise.
But talking to Total Film, she refused to let even the smallest detail slip: 'I signed a blood oath... [Raising her hands] Bloody thumbprint on the paper.'
However, she did open up about what attracted her to the part.
'I went after it because it was the best role and Chris was willing to meet me,' she said.
'I want to be the best actress I can be and that means working with the best people and taking the most challenging roles. That's the plan and so far it's led to some really exciting places.'