http://www.bbc.co.uk/news/uk-politics-36709218
Theresa May, Andrea Leadsom, Michael Gove, Stephen Crabb or Liam Fox.
Place your bets for the first to be asked to step on the trap-door. My hunch is it'll be Fox in the firing line, but for no particularly strong reason.
Profile snippets below are from the BBC's site, linked to from the one above.
May:
Where she stands on Brexit: Backed Remain campaign but says vote to come out must be respected. "Brexit means Brexit. The campaign was fought, the vote was held, turnout was high and the public gave their verdict. There must be no attempts to remain inside the EU, no attempts to rejoin it through the back door and no second referendum." Mrs May also said there should be no general election before 2020 and no "emergency" Brexit budget - and that she would abandon the target of eliminating Britain's Budget deficit by the end of the decade - a day before the chancellor himself abandoned it.
Leadsom:
Where she stands on Brexit: She campaigned to get Britain out of the EU and has described the referendum result as "a huge opportunity for our great country". She believes in scrapping free movement and wants free trade negotiations with the rest of the world. She told Sky News: "My personal view, very genuinely, is the next leader is someone who has to deliver on the promise of the referendum because they can see the huge advantages and they believe in them. I think it's very difficult for somebody who campaigned to stay in, who thinks that there will be disaster if we leave, to suddenly turn it around and start believing we can make a go of it."
Gove:
Where he stands on Brexit: "The British people voted for change last Thursday. They sent us a clear instruction that they want Britain to leave the European Union and end the supremacy of EU law. They told us to restore democratic control of immigration policy and to spend their money on national priorities such as health, education and science instead of giving it to Brussels. They rejected politics as usual and government as usual. They want and need a new approach to running this country.
He ruled out a snap general election if he becomes PM - and he said he would abandon Chancellor George Osborne's target of eliminating Britain's budget deficit by 2020. Mr Osborne himself has since abandoned the target.
Crabb:
Where he stands on Brexit: He campaigned to remain in the EU but now says: "We had a clear result from the referendum. And the result was for the UK to leave the European Union. There can be no stepping back from that." Has ruled out a second referendum.
Mr Crabb has set out three aims for the EU negotiations: Controlling immigration, "as close an economic relation with the EU as we have now" and "end of the supremacy of EU law".
Fox:
Where he stands on Brexit: "I do not believe there is room for membership of the single market if it entails free movement of people. Those who voted to leave the EU would regard it as a betrayal and frankly they would be right. We do not need to be part of the single market to sell into it. Countries like the United States manage to do that very well. It is in our mutual interests to have a free and open trade relationship with our European partners but we cannot accept the concept of free movement of people as its cost."
