Lucy, now played by Hetti Bywater, doesn't like the look of Mandy from the moment that they're introduced later this week - and things get worse when the ex-stripper interrupts valuable bonding time between her and Ian.
When Lucy decides that she wants to be number one in her father's life again, she realises that her best plan of action will be to get close to Mandy (Nicola Stapleton) while secretly plotting against her.
Mandy soon falls for the plan as she heads to the pub with Lucy, who manipulates her into thinking that she's a "cool older sister" rather than a wicked stepmother.
© BBC
© BBC
Pictured: Mandy enjoys her 'bonding time' with Lucy.
Lucy then tries her luck with her dad's girlfriend by asking her to get hold of some pills for the two of them, and Mandy is so keen to stay in her good books that she agrees.
Mandy ends up thinking that everything has gone swimmingly with Lucy - but the mischievous teenager later pockets the pills with an idea in mind.
The next day, Lucy engineers it for Bobby to find the pills - knowing that Ian (Adam Woodyatt) will be furious with Mandy when he finds out. Will Lucy succeed in her attempt to set up Mandy or will her scheme backfire?
EastEnders airs these scenes on Monday, January 16 and Tuesday, January 17 on BBC One.
> EastEnders announces Lucy Beale return
> EastEnders: Meet the new Lucy Beale - Pictures
> EastEnders' Nicola Stapleton promises Lucy return drama
> EastEnders' Mandy is no fool with Lucy, says Nicola Stapleton
> Read more EastEnders spoilers and news
