Of all the unhappiness my divorce has brought upon me, loneliness has never been in the least a part. Lack of company in the evening is to me an absolute luxury.

Thus does Vicky, a young divorcée in London with a small daughter to support, reassure herself.

But as the plucky courage of the early days of World War II gives way to the fatigue and deprivations of its middle, company in the evening is just what she gets. To the chagrin of her housekeeper, Vicky agrees to take in a pregnant, widowed sister-in-law (“Talking to her is like walking through a...