Spoiler alert about episode two of Collateral, which is on tonight on BBC2 at 9pm

Carey Mulligan has said that the cop she plays in BBC2’s hit thriller Collateral may not break the rules but she’s certainly prepared to bend them as she makes a big breakthrough tonight.

Carey stars as Detective Kip Glaspie, who’s hunting for the murderer of a pizza-delivery man and tonight she susses out that the killer is a woman – check out our who’s who guide to the drama.

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Desperate for more answers, Kip goes back to the sister of the murder victim, an illegal immigrant from Syria, yet is shocked to learn she has been taken away to an immigrant detention centre.

When evidence surfaces showing the killer had connections to the Army, the detective begins to suspect this was no random act of violence, but something more sinister.

“This case means a lot to Kip,” said Carey. “She’s not a rule-breaker, but she does believe in bending the rules to do the right thing. She would never do anything terrible or illegal, but she is going to put her neck on the line if she thinks the result could be big enough!”

Collateral continues on BBC2 tonight at 9.00pm.