He needs to call Nick Clegg and offer him the following improvement on the existing offer - two seats at cabinet for him and Vince Cable, one of them being that of the Prime Minister. And insists that he or Darling, with Cable's assistance, ride out the financial crisis.
Brown then makes a public speech acknowledging he has been rebuffed as PM, and offers the public change they can believe in - a Clegg-led administration, heavy on the Labour ministers, but with the addition of Clegg and Cable.
And he offers his own expertise as Chancellor to steer Britain out of the crisis with Cable's help.
He then steps down to cabinet and does just that, the one thing he does well - manage the economy, alongside Cable. The markets would believe in that team.
Gordon could step down, and will do if Cameron puts a deal together. It will be the cruel end that most politicians suffer. But there is the chance to stay in the game, redeem his reputation and do the state some service.
He should offer Clegg the poisoned chalice of sitting in Number 10, holding together a rainbow alliance, and the chance to implement their policy in Government.
He should enjoy this one last victory over the Tories and over Mandelson, who would take no part in such a cabinet and would be banished to the Lords, which would then be immediately overhauled.
And he should take this chance, this last stand, to redeem his legacy with one last masterful stint at the job he's good at, rather than the job of Prime Minister.