Just a fluffy romance, only good because Rinehart is good at pacing and foreshadowing; but in passing, as a plot-bunny, a reminder of what life was like before universal inoculation. The butler took sick and dropped a tray, and the servants are mysteriously all missing, and:
There was a man on the top step, with his mouth full of tacks, and he was nailing something to the door, just below Jim's Florentine bronze knocker, and standing back with his head on one side to see if it was straight.
"What are you doing?" Jim demanded fiercely, but the man only drove another tack [...]
It said "Smallpox."
They're all locked into a house together under police guard, because one person taken out of the house may have smallpox. This is not necessarily a brief sentence:
...keeps the commuter at home for three weeks with the measles; that makes him get the milk bottles and groceries from the gate post and smell like dog soap for a month afterward, as a result of disinfection.
Before that, a combination of mob attacks, walled cities, and general Decameron-style flight to places previously uninfected.
Project Gutenberg etext #1671, When A Man Marries
So wrote clew in Fiction (20th c.).