The Prime Minister's Secret Agent by Susan Elia Macneal (Maggie Hope series book 4)

This is the fourth installment of the Maggie Hope series

Summary
-Maggie is ready for some R&R. She finds that on a Scottish isle, home to the training camps which trained her for MI-5 work. Instead of rest and relaxation, she is, once again, drawn into a mystery. Three ballerinas, including one of Maggie's closest friends, Sarah Sanderson, fall victim to a mysterious illness which leaves oozing black blisters. As she investigates, it turns out that the oozing black blisters are a result of exposure to anthrax. She soon discovers that the Prime Minister is hoping to develop bioweapons to use against Britain's enemies. But taking attention away from this are the struggles in the Pacific with the Japanese.