What's going on?
Allegations of a child abuse ring in Westminster in the 1980s are leaving parliament facing a huge scandal, its biggest for years. At the heart of the issue is the suspicion of an establishment cover-up - which makes it all the more painful that the present government is resisting calls for a full public inquiry.
OK, let's start at the beginning. Where do the allegations come from?
A man called Geoffrey Dickens. He used to be the MP for Littleborough and Saddleworth. In 1983 he is supposed to have passed a dossier to the home secretary of the time, Leon Brittan. Dickens' son, Barry, says of the dossier: "It was talked about in the family, discussions now and then, sort of 'Wait and see what happens - this is going to blow everything apart. These people won't know what hit them'."
What was in the dossier?
We don't know. Dickens died in 1995 so we can't ask him. Tom Watson, the Labour backbencher, wanted to find out the answer. In March 2013 he raised a query with Mark Sedwill, the new permanent secretary at the Home Office. Sedwill - the most senior civil servant in the department - asked "an experienced investigator from HMRC who normally works outside London" to look into it.
And what did this unnamed investigator find out?
Not much. The review's methodology worked through four stages. They looked for files. They looked into files some more. They looked for more files. They looked in other places for more files.
And they found...?
We don't know for certain because the report itself hasn't yet been published (Labour are now calling for it to be made public). The executive summary was released, though. It stated: "The review found no record of specific allegations by Mr Dickens of child sex abuse by prominent public figures." But it then added: "While copies of Mr Dickens' letters were not retained, the investigator did find files referring to them."
What does Brittan have to say?
He wasn't asked about it - officially, at least - but he did give a statement shrugging the whole thing off afterwards. This confirmed he wrote a letter to Dickens on March 20th 1984 explaining what had been done in relation to the files. Brittan said recently: "Whilst I could not recall what further action was taken 30 years ago, the information contained in this report shows that appropriate action and follow-up happened."
So that's that?
Not really. We don't, and can't, know for certain what happened because there are too many unresolved questions. This first Home Office review didn't interview former ministers or officials - it just sought to establish what the paperwork situation was. And it was conducted by an individual who can't even be named by the Home Office. That hardly inspires public confidence.
But if the Home Office's filing system is robust and working properly, the government won't have to bother any more with this one, will they?
As it turns out, the Home Office's filing system is far from robust. Sedwill has revealed, in a letter to the Commons' home affairs committee chair Keith Vaz, that 114 "potentially relevant files" have been "destroyed, missing or presumed not found".
SO they've lost files relating to allegations of what could be one of the biggest cover-ups in Westminster of the 20th century?
Yes. What's more, something is clearly up. It's also now emerged that as a result of last year's report four cases of historic sex abuse were referred to the police.
So how are politicians in Westminster responding?
They're seeking the truth - and they're not convinced they're anywhere near it right now. The lead campaigner now is Simon Danczuk, the MP for Rochdale, who raised details about the Dickens dossier to MPs on Tuesday. In his view the disappearance of the files "suggests either incompetence on a wide scale or a massive cover-up".
Surely the government can't get away with not doing anything more.
No - which is why David Cameron has now stepped in. The prime minister asked Sedwill to "provide further assurance" that last year's review had been "appropriately actioned". That, of course, is Whitehall speak for 'not being utterly messed up'. So what Sedwill has decided to do is to get someone else to have a look at it. "I will engage a senior independent legal figure to assess whether the review's conclusions remain sound," his letter declares. Cameron's decision that a 'review of the review' is necessary is being taken as an acknowledgement that last year's one is inadequate.
I expect the opposition are up in arms?
Shadow home secretary Yvette Cooper has been on manoeuvres, that's for sure. She has a shopping list of demands on the government - making sure the police know everything they need to, etc. But she's not quite there in terms of calling for a full public inquiry just yet. "The home secretary doesn't seem to have grasped the gravity of this and so officials and Downing Street have not yet taken the action we need," she says.
Are ministers being bugged about it much?
It was the first question asked to education secretary Michael Gove on The Andrew Marr Show this morning. Gove ruled out a public inquiry outright. His language was thoroughly defensive. "The most important thing we need to do is make sure the work we do is proportionate and focused," he said. Gove called on people with specific concerns to bring their allegations to the police. He said his department was reviewing the measures in place to keep children safe now but pointed out these allegations related to a different time, "when a different culture prevailed".
So what happens now?
The question-marks have to be resolved - urgently. Because this isn't the kind of scandal about a single individual doing dodgy things in order to get more money. It's not a case of a rogue politician being 'out for themselves'. It's about allegations of powerful people conspiring to carry out child sex abuse. In these circumstances, the cover-up is an essential part of the story. So how the government handles it - and how it handled it in the past - matters.