Were child abuse inquiries blocked?
It's not so much a single scandal as a series of claims relating to the alleged activities of child abusers from the 1960s through to the 1980s.
Furthermore, it's alleged that investigations into the abuse were thwarted or dropped to protect the perpetrators, some of whom were powerful people or had links to the powerful.
It's not just about the "Dickens Dossier" of allegations passed to the Home Office in the 1980s. It's not just about the Paedophile Information Exchange (PIE), which campaigned to legalise sex between adults and children.
It goes further than Cyril Smith's alleged abuse of children 40 years ago. And it extends beyond a police investigation into the rape of children at a guest house allegedly frequented by politicians and celebrities in the 1980s.
But linking it all is a common thread - the vulnerability of some children in care and a failure to properly investigate and hold to account those responsible for their abuse.
One year to start with is 1994. Back then a man called Peter McKelvie was a child protection manager in Hereford and Worcester who was assisting police investigating an influential paedophile, Peter Righton.
Righton had hoodwinked social workers and child abuse specialists during his career rise to become a consultant to the National Children's Bureau.
Now dead, he was ultimately convicted of importing child pornography. But Mr McKelvie believes that what was discovered went much further than that and Righton should have been convicted for far more serious crimes.
For 20 years he says he has been asking himself why leads suggesting links between paedophiles and government were not investigated further by police.
When the Jimmy Savile scandal broke in 2012 Mr McKelvie took his concerns to Labour MP Tom Watson. When Mr Watson raised it in parliament, a police inquiry, Operation Fairbank, was launched to examine the claims.
Officers tracked down seven boxes of evidence from the original Righton investigation and started to go through them. The resultant publicity prompted more calls from members of the public to Mr Watson.
As more information came in, different investigations were launched, the best known being Operation Fernbridge which has been investigating allegations that in the 1980s famous people abused children at a place called Elm Guest House in Barnes, south-west London.
Meanwhile in Rochdale another Labour MP, Simon Danczuk, was looking into claims that Cyril Smith had abused children with impunity at a residential care home, Knowl View.
It was his evidence to the Home Affairs Committee last week, calling for an investigation into the "Dickens Dossier", that catapulted a series of claims into the headlines.
Peter Righton was a member of the Paedophile Information Exchange (PIE), a shadowy pressure group which in the 1970s and 80s tried to legitimise and decriminalise sex between children and adults.
It no longer exists but achieved notoriety once more earlier this year with reports that in the 1970s it had infiltrated the National Council for Civil Liberties. Did it infiltrate government too?
A man claiming to be a former Home Office civil servant last week told the Sunday Express that not only was PIE receiving funding from the Home Office in the 1980s, it was doing so at the request of Special Branch, the intelligence-gathering arm of the police. And he believed the police were not interested in catching child abusers.
He said his superior told him that Special Branch "found it politically useful to identify people who were paedophiles... I was aware a lot of people in the civil service or political arena had an interest in obtaining information like that which could be used as a sort of blackmail."
Home Secretary Theresa May has said a Home Office review found the claim that PIE was government funded to be untrue but it would be re-examined by the inquiry.
Allegations of Special Branch involvement in a cover-up were also made by Jack Tasker, a former Lancashire detective who tried to prosecute Cyril Smith for child sex abuse.
He says Special Branch detectives arrived in his office one day, told him to hand over all his notebooks and files, and told him to go no further with his investigations.
"Nothing like that had ever happened before," he told the BBC. "That came from London." Cyril Smith was never prosecuted.
If these allegations are true, the newly commissioned inquiry into abuse has a lot of work on its hands.