Here is your 10-point cheat-sheet for this big story:
The former Home Secretary claims Mr Shinde's alleged malpractices included encouraging and facilitating corruption in the assigning of important police posts.
Mr Singh says that contrary to what Mr Shinde said last week, the US has offered no help in tracking down terrorist Dawood Ibrahim and bring him back to India from Pakistan.
"Even if an agency belonging to another country agrees to help us in a mission on a third country's soil, this should not be made public. The FBI has made no such commitment, at least as long as I was there. Dawood is in Pakistan, under ISI's protection and to say he will be arrested with the help of FBI is ridiculous," he said on Tuesday. (Dawood Ibrahim in Pakistan, joint efforts with US to nab him: Sushil Kumar Shinde)
Mr Singh, who retired as Home Secretary in June, has also accused the Home Minister of shielding a Mumbai-based businessman close to Dawood Ibrahim and preventing the Delhi Police from interrogating him in connection with match-fixing in the Indian Premier League.
He claims that the same businessman is linked to the telecom or 2G scam, and that Mr Shinde tried to protect him in that scandal as well.
Mr Singh joined the BJP last week and is allegedly interested in running for parliament from Bihar.
"If Mr Shinde is found to have intervened in the match-fixing probe, he needs to be sacked immediately," said the party's Ravi Shankar Prasad.
But the Congress and others have asked why Mr Singh chose to keep his silence when he was in office if he was aware that his boss was violating rules.
Why did he not put it on record when he was in service? Why did he not meet the Cabinet Secretary and PM?" asked union minister Manish Tewari.
Former top cop and anti-corruption activist Kiran Bedi made a similar point, "What did you do as the Home Secretary? Did you tell the PM of the unlawful instructions? If not then you're at fault. If you get any unlawful orders complain to the higher officials. Don't say things after retiring."
Theft At Official Residence Of Congress MLA Jaivardhan Singh, Cash Stolen: Cops "Neither Tired Nor Retired": Bhupinder Hooda On Next Haryana Chief Minister Trinamool Vs Ex Women's Panel Chief Over Kolkata Doctor's Rape-Murder Mamata Banerjee's Sunday Ultimatum To CBI For Death Penalty In Rape-Murder How Extreme Weather Is Leading To Rise In Child Marriages In Pakistan "Prove With Pics Crime Scene Intact": Court To Bengal Over Hospital Vandalism Gujarat PGCET 2024 Revised Admission Schedule Released, Check Details Hrithik Roshan, Priyanka Chopra Join Call For Justice In Kolkata Rape Case Sexual Assault Attempt On Coimbatore House Surgeon Sparks Protest Track Latest News Live on NDTV.com and get news updates from India and around the world.