Who knew that an alleged Chinese spy was arrested back in March?
No. 10 won't tell us when the prime minister found out. Neither will the government reveal whether or not the Foreign Secretary, James Cleverly, knew when he visited Beijing last month.
But there are MPs who want to know why they weren't told that a parliamentary researcher had been arrested for allegedly passing information to China.
This afternoon, the Speaker of the House of Commons said that "the extremely small number of people who needed to know were briefed on a strictly confidential basis."
It's thought that this may have included the Speaker himself and Alicia Kearns, the Chair of the Commons Foreign Affairs Committee, who is understood to have sponsored the researcher's pass.
It seems unlikely that the researcher - who strenuously denies the accusations - would have had access to classified information.
But amongst the concerned MPs are a number who have already been sanctioned by China for their outspoken views on Beijing's behaviour and who may have had sensitive information crossing their desks.
Sir Iain Duncan Smith is part of that group.
The PM must reveal what he knew about Westminster's alleged Chinese spy, said Labour leader Sir Keir Starmer
He says he deals with Chinese dissidents, particularly from Hong Kong, who might not want the Chinese Communist Party knowing their details.
Back in February - just before the researcher was arrested - he showed me some fake emails purporting to come from him.
The emails were falsely announcing his resignation from the Inter Parliamentary Alliance on China, a group critical of Beijing.
They appeared to have been sent from an IP address in Hong Kong.
So MPs critical of China are being targeted by, or on behalf of, the Chinese government.
That is why they feel they should have been told much sooner if there was a security risk inside Parliament.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know...