On a podcast I listened to Wednesday morning, Henry Zeffman, a politics reporter at The Times of London, described trying to sketch out possible outcomes on the back of an envelope, switching to a larger envelope, and throwing up his hands. “I thought, superficially, ‘Oh, O.K., this is relatively straightforward,’ and suddenly I was overwhelmed — my artistic and design skills are not brilliant, and there were lines going in all sorts of directions between boxes of all sorts of shapes and sizes,” he said.

All of which is to say: Don’t worry if you’re confused. At the London bureau of The New York Times, we sweat paracetamol.

If Mrs. May’s plan is voted down on Tuesday, five things could happen.

(1) She could go back to Brussels later in the week and negotiate face-saving changes to the current plan; (2) the government could pivot to a softer Brexit known as the “Norway model”; (3) the government could plunge toward a “no-deal” Brexit, with potentially severe economic costs; (4) the country could hold a second referendum, risking the fury of the Britons who turned in a 52 percent majority in favor of leaving the E.U.; or (5) the country could hold a new election.

Thursday is the third of five days of debate in Parliament leading up to the vote. Since the proceedings are streamed live (right here), it is a good opportunity for newcomers to eavesdrop on the House of Commons. It features a hilariously pompous speaker, John Bercow — “It is a point so blindingly obvious that only an extraordinarily clever and sophisticated person could fail to grasp it,” he once chided a member — and a braying, mooing barnyard symphony of partisan heckling noises.

Mrs. May, nothing if not dogged, has weathered rounds of pummeling since mid-November, when she made her withdrawal agreement public.