Alfie Moon (Shane Ritchie) has been keeping his financial woes a secret from his family and he soon sets into motion a sequence of events that will be catastrophic for all.
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Shane Ritchie as Alfie Moon in Eastenders
Long-time Eastenders favourites The Mitchells are also going to feature heavily in the coming months, as Phil Mitchell (Steve McFadden) realises his fiancée Sharon is planning to defraud him after their wedding.
Never one to sit back, Phil and old flame Shirley decide to take revenge, but the return of Phil's son Ben from prison will make things harder for Phil.
In a statement the show's producer Dominic Treadwell-Collins said: "Bombs that we have been carefully planting over the last few months are about to explode all over the Square as some of our most iconic characters’ lives change forever.
"With huge twists, shock returns and stories which will move, provoke and entertain, this September is going to be classic EastEnders and an unforgettable start to our autumn."
Ronnie Mitchell will also return to Walford, which was promised by the soap's producer late in 2013.
Speaking at an Eastenders party, Dominic Treadwell-Collins said at the time: "... Ronnie will have a big story. The question with Ronnie is, 'Is she her father's daughter?' I think we're going to see with Ronnie how someone becomes a villain. I keep talking about Darth Vader - the making of a villain. Not a soap bitch, but a villain."
It's been a year of ups and downs for the long-running BBC soap which has been hit by a ratings slump and has been bested by ITV soap Coronation Street for several years in a row at the National Television Awards.