SPOILER ALERT: Lauren Branning makes shocking discovery as Lucy Beale murder plot reaches climax... after accepting Peter Beale's marriage proposal in EastEnders

PUBLISHED: 08:45, 5 February 2015 | UPDATED: 14:15, 5 February 2015

Marriage plans take a backseat on Thursday evening as Lauren Branning makes a shocking discovery that will push viewers’ one step closer to the identity of Lucy Beale’s killer.

The Albert Square resident will stumble across evidence missing from recently deceased DCI Emma Summerhayes’ case file relating to Lucy’s murder.

Lauren, played by Jaqueline Jossa, will later attempt to solve the case on her own by attempting to access Emma's phone by guessing the password.

Scroll down for video

Drama: Marriage plans take a backseat on Thursday evening as Lauren Branning makes a shocking discovery that will push viewers’ one step closer to the identity of Lucy Beale’s killer

The detective had previously solved the case, but was struck by a car and later died in hospital before she had a chance to expose the killer.

l shock her to the core, viewers will have to wait before the protracted storyline reaches its climax.

The daughter of Max Branning - one of the prime suspects - had previously been celebrating her engagement to boyfriend Peter Beale, played by Ben Hardy.

Discovery: The Albert Square resident will stumble across evidence missing from recently deceased DCI Emma Summerhayes’ case file relating to Lucy’s murder

The latest development comes as the storyline reaches fever pitch ahead of the 30th anniversary episode, in which the killer will finally be revealed to the nation.

It follows the BBC's creepy trailer for the reveal, which showed Lucy as a ghost looking down at Albert Square.

The trailer follows on from the clue revealed at the National Television Awards that the last thing Lucy heard before her death was the sound of her music box.

Will you marry me? Peter Beale proposed to Lauren in the Queen Vic on Tuesday evening

With this ring: The show regular presented his girlfriend with a diamond engagement ring

There are currently 14 suspects in the 19-year-old's murder including brother Peter and father Ian.

Lucy, who was played by actress Hetti Bywater, was murdered in one of the BBC One soap's biggest murder plot lines in April, last year.

Her murderer will be revealed at the end of this month and characters including Max and Abi, played by Jake Wood and Lorna Fitzgerald respectively, have been cited as possible suspects.

Even Lucy's step-mum Jane Beale, played by Laurie Brett, could be involved.

'The Week of Revelations': Eastenders' new trailer (related)