The prime minister's secret agent : [No. 4 : Maggie Hope mystery]

Summary: Maggie Hope has returned from her undercover mission in Berlin with scars not just on her body but on her soul. Instead of going on another Special Operations assignment in war-torn Europe, she returns to one of her old spy training camps in western Scotland, this time as a teacher. But instead of the tedium Maggie is expecting, she's drawn against her will into another web of danger, this time involving a terrifying biological weapon secretly developed and stockpiled by Churchill for the anticipated Nazi invasion. Maggie's failure to solve a series of deadly poisonings could endanger the lives of the entire British civilian population--but what will be the cost of success?