The novel opens with Captain Christopher Tietjens, ably helped by Sergeant-Major Cowley, trying to move a draft of 2,994 troops, among them a contingent of Canadian railway workers, from a base camp in Rouen to the trenches at the front.

His efforts are blocked by having orders given and then countermanded; by having inadequate supplies for these troops from a quartermaster who profits by holding them back; by contending with a French railway strike meant to prevent the withdrawal of British troops from the front but which also prevents them from being sent to the front; and by fighting the interference of the British Garrison Police, who constantly harass the Canadian volunteers whom they willfully and mistakenly take for conscripts.

Moreover, General Lord Edward Campion, Tietjens’ godfather, has assigned to his godson's staff the shell-shocked and intermittently mad, though highly decorated, Captain McKechnie, a classical scholar and proud of it.

This becomes more urgently the case when Levin tells Tietjens that the woman in the general's car who is waiting to see him is Sylvia herself, who has pursued him across the Channel without passport or papers.

He focuses particularly on Sylvia's parting from him some ninety-eight days ago by ordering a taxi to take her to Paddington Station at 4:00 a.m. to catch a train to Birkenhead where she will enter into a nearby convent of Premonstratensian nuns for a long, if not a permanent, retreat.

This to Tietjens is a sign that she is putting an end to their marriage and that he is free to pursue Valentine, whom Sylvia has contrived to have meet him the night before he leaves for France.

Tietjens has time to reminisce on these matters because, although Sylvia had been waiting in the general's car to see him, she has had herself driven away without saying a word to her husband.

These things get done in the face of what Levin tells Tietjens about the problems that Sylvia has caused General Campion, who will not stand for having “skirts” in his encampment.

Tietjens nevertheless gets his draft bedded down, even as he sees more trouble brewing with General O’Hara's police who deliberately keep some of his Canadian volunteers from getting back to base on time and then arrest them.

In addition, he learns that Lord Beichan, a newspaper magnate, has placed a Veterinary-Lieutenant Hochkiss in charge of “hardening” horses, and Tietjens will not stand for such brainless brutality.

Although she has made an appearance in I.ii, where she is seen looking through the window of General Campion's automobile, Sylvia Tietjens is fully present and dominates this chapter by commanding all around her by her stunningly beautiful presence in "the admirably appointed, white-enamelled, wickerworked, bemirrored lounge of the best hotel" in Rouen.

Sylvia's supposed purpose in coming to Rouen is to have Christopher sign a document, which requires no signature, that gives her the legal right to live at Groby, his family's ancestral home in Yorkshire, and makes their son Michael successor to it.

Meanwhile, Campion has temporarily suspended O'Hara as chief of the Garrison Police and has given Perowne a choice between rejoining his regiment at the front or a court-martial.

But in spite of these confusing and exhausting events, Christopher has got his draft off to the front early that morning, proving once again his extraordinary competence as a commanding officer.

He cannot put Tietjens on his staff because that would smack of nepotism; he cannot assign him as a liaison officer to the French army because the lies written in his dossier by Colonel Drake, Sylvia's former lover, who accused him of being a French spy, prevent it; he cannot assign him to Transport, as his brother Mark requested, because Christopher would then be answerable to Veterinary-Lieutenant Hotchkiss, who brutalizes horses under the orders and protection of Lord Beichan.

With these matters settled, the novel ends with the Godhead inspecting Tietjens’ cook-houses, presented as a cathedral, where Sergeant-Cook Case presides as high priest.