Here's your 10-point cheatsheet to this big story:
Sonia Gandhi reached the ED office accompanied by her son Rahul Gandhi and daughter Priyanka Gandhi Vadra at 11 am. Medical staff were kept on standby and her daughter, Priyanka Gandhi Vadra, waited throughout in case she needed medical attention.
The questioning of the Gandhis has stirred up the Congress, which held massive protests. The police said 57 MPs, including Rahul Gandhi, were detained while holding a march from Parliament to Vijay Chowk.
Some of the Congress leaders, including Youth Congress chief BV Srinivas, were seen to be manhandled during the detention. A video of Mr Srinivas being pulled by his hair was widely circulated on social media. The police said disciplinary action will be taken against the erring officials.
Leader of the Opposition in Rajya Sabha Mallikarjun Kharge alleged that he, along with other Congress MPs, was manhandled as well. This, he said, was done at the behest of Prime Minister Narendra Modi and Union Home Minister Amit Shah.
Rahul Gandhi, who was questioned in the case last month for more than 50 hours spread over five days, said India is now a "police state". "India is a police state now, that's the truth. PM Modi is a king, and this is a police state. What will happen if MPs cannot meet the President?" Mr Gandhi told reporters while he was being detained.
Mr Gandhi and the other MPs had assembled in Parliament and were marching towards Vijay Chowk on their way to the Rashtrapati Bhavan to draw President Droupadi Murmu's attention to the alleged misuse of central agencies, when they were stopped by the police. "The country's 'King' has ordered -- whosoever asks questions on unemployment, inflation, wrong GST, Agneepath -- put them in jail," Mr Gandhi tweeted.
The questioning of the Gandhis comes amid parliament's Monsoon Session where the opposition is trying to highlight several issues including inflation. Over the last two days, 23 MPs – four from the Lok Sabha and a record 19 from the Rajya Sabha -- have been suspended from the two houses of parliament.
Mrs Gandhi was apparently asked over a dozen questions on Day One. She is understood to have been asked questions on her involvement with the National Herald newspaper and the Young Indian Pvt Ltd, reported news agency Press Trust of India quoting sources.
The Enforcement Directorate is expected to match her statement with that of Rahul Gandhi as both are majority stakeholders in Young Indian, officials said.
Denying any wrongdoing, the Congress has maintained that the Young Indian is a "not-for-profit" company and so, there can be no question of money laundering.
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