While Zara looks forward to Adam’s return from America, Emma is shocked to find Gareth taking drugs. She offers to talk to him about his problem but while she’s distracted, Gareth leaves Emma’s house. Gareth talks to Adam on the phone and confesses that he is in distress but Adam is too full of his professional success to really listen.

Gareth is made angry and bitter by his brother’s dismissiveness, and in a coke-fuelled fit of vengefulness goes around to Zara’s house.

Zara, waiting for Adam and dressed to seduce, assumes that Gareth is his brother and kisses him.

Gareth responds but when Zara realises that something is wrong he persists and Zara is horrified to realise that Gareth is impersonating his twin.

When Gareth takes things too far Zara is forced to defend herself and stabs him.

In the aftermath of the attack Zara deals with the effects, Rob goes on the hunt for Gareth – but will Adam get to his evil twin before the police…?

Doctors air these scenes from the 12th December on BBC One.