"With All Due Speed" is an extra of about 20k words, covering the period from when Thesan Wain and Isembard Fortier begin discussing an actual engagement through to their wedding (the summer of 1925 through late December 1925), following the events of Eclipse.
July 7th, 1925: Isembard realises he would like to move toward marriage sooner rather than later.
August 6th: Thesan talks with Seth and Golshan about Isembard's visit to her parents and their plans.
August 10th: Isembard talks to his brother Garin about what he intends to do (and finds out more about Garin and Livia's marriage.)
August 17th: Isembard proposes and Thesan joyfully accepts.
August 21st: Discussions about rooms at Schola, and the implications of space and resources.
November 11th: Isembard returns from the Armistice Day memorials, having had an unexpected encounter with Seth and Golshan (their meeting is part of Tea and Meetings.)
December 1st: Isembard visits Thesan's parents, and her father offers advice on a marriage.
December 2nd: Thesan and Isembard get a chance to discuss that visit and the (vast) differences in their families.
December 12th: Thesan and Isembard have dinner at Arundel with Livia, Garin, and Alexander.
December 23rd: The wedding (one section from each of their points of view). Includes a couple of particular wedding customs from Thesan's family.
December 28th: Sorting out how they mean to go forward with certain obligations.