In Among the Mad, our psychologist-detective heroine works with Special Branch forces in a race to find a terrorist (though I'm not sure they had that term in 1931). With still-shell-shocked veterans being released onto the streets at the beginning of the Depression, someone intends to set off a gas bomb on New Year's Eve at St. Paul's. But, like the anthrax attacks 70 years later, the particular gas used as a warning is military-grade. It's a decent thriller, and sets up the reader for Maisie's involvement with Special Branch or other intelligence-gathering efforts later.
The Mapping of Love and Death actually had more significant character development and drama: Maisie's mentor dies, she strikes up a relationship with her old employer's son, her briefcase (a gift from her fellow servants when she went off to Cambridge, symbolizing her working-class, pre-war past) is stolen. The case at the center of the book is fascinating as well: the role of cartographers in World War I. The remains of a cartography unit listed as missing in 1916 are recently discovered, and an autopsy suggests an American mapmaker in the unit was murdered. One of the characters from the first book in the series also makes an appearance, making the plot ends come full circle. It's as if Jacqueline Winspear is collecting bits of the past in order to set readers up for an entirely new Maisie. I certainly hope so!