Boris Johnson turns out after all to be a Russian asset.
He is exposed after a coded memo he writes promoting Christopher Pincher MP, is decoded.
The memo shows that when he promoted Mr Pincher he knew the MP was subject to an investigation over sexual assault. It also shows that he lied to Parliament when he said he was not aware of the allegations and the investigation.
The giveaway though is that the memo is shown to be written in a code used by the Russian FSB.
Boris Johnson’s downfall is brought about by his unforced error in using that code, which he does in disregard for how it might reflect back on him and which he does to show off his dexterity and for the rush of playing with fire.
Boris Johnson’s motive is political. He dreams of resurrecting the Ottoman Empire but is gullible and falls for an obvious Russian ploy in which the FSB promise him £350 million a week indefinitely to support his political dream once he has extracted Britain from the European Union.
Johnson’s exit causes him to start to spill the beans, first by leaking a video of a partygate party at CCHQ then by leaking stories that imply his relationship with former Russian agents who might still in fact be active.
The stinger in the tail is when it turns out that Michael Gove is his handler.