Murder in the Mews is a Poirot short story written by Agatha Christie and first published in March 1937.
Bonfire Night (also called Guy Fawkes Night, Guy Fawkes Day, and Firework Night), is annually observed on 5 November in Great Britain to commemorate the events of 5 November 1605, when Guy Fawkes, a member of the Gunpowder Plot, was arrested while guarding explosives the plotters had placed beneath the House of Lords; people lit bonfires around London in celebration of the fact that King James I had survived the attempt on his life.
The mews in question are Bardsley Garden Mews
Laverton West takes a call from the Prime Minister. As the episode takes place in November 1935, Stanley Baldwin would be Prime Minister.