Archie Mitchell's killer will be told of their guilt only 30 minutes before tonight's live episode of EastEnders is broadcast, soap bosses have revealed.
Stars will be in the dark until almost the last moment about whether they sparked one of the BBC1 soap's biggest ever whodunnits.
Scriptwriters have penned 10 possible endings to the episode, with each of the different suspects rehearsing their scene unaware of which will make the show.
The first ever live episode is to mark the soap's 25th anniversary, and brings to an end the guessing game which began when Archie (Larry Lamb) was bumped off in the Queen Vic on Christmas Day.
Possible culprits include Peggy Mitchell (Barbara Windsor), Janine Butcher (Charlie Brooks), Ian Beale (Adam Woodyatt) and Bradley Branning (Charlie Clements), but the entire cast is still clueless about the identity of the guilty party -- and EastEnders bosses stress it could be anyone.
Archie was bludgeoned with a bust of Queen Victoria in the Albert Square pub after alienating many of the residents.
In an attempt to keep the outcome under wraps, executive producer Diederick Santer will not reveal the truth to the cast member in question until just half an hour before the episode transmits.
EastEnders fans are desperate to know who the killer is, and bookmaker William Hill said a total of £1m (€1.14m) was expected to be wagered on the outcome.
In its latest odds, the firm put Sean Slater (Rob Kazinsky) as favourite at 4/7, even though the character has not been seen in the show since January 2009.
Santer, who has been planning the episode for nine months, upped the excitement levels by revealing that so far there have been three clues as to the killer's identity -- one of them in the Christmas Day episode, one midway through the investigation and a final pointer which he enigmatically said was not necessarily in the programme.
The cast have taken part in one read-through, two full dress rehearsals, three days of standard rehearsal and a technical rehearsal in the run-up to the big day.
Three golf buggies will be on hand to transport cast between sets, and there will be 36 camera operators, rather than the usual four. A total of 13 make-up artists, 12 wardrobe staff and 16 props people will work on the episode, and 7.5km of cable will be used in bringing the show to TV screens.
There will be a slight time delay before the episode appears on screen in case of difficulties, though a soap spokeswoman stressed it would be "a matter of seconds".