The Prime Minister's Secret Agent by Susan Elia MacNeal

It's November 1941 and both the British and Americans have intel that the Japanese might be planning some type of attack in Hawaii. The British would be thrilled with an American entry into the war, since their help is desperately needed in fighting Hitler. Meanwhile, in the north of Scotland, Maggie Hope is working--training spies and trying to keep depression at bay after several traumatic events in her personal life. When her good friend, Sarah, falls deathly ill in Edinburgh, Maggie, along Mark Standish from MI-5, works to uncover what happened to Sarah, although some are trying to hide the cause of Sarah's sickness. In this fourth book of the Maggie Hope series, MacNeal frames her book with the imminent attack on Pearl Harbor and moves the personal stories of Maggie and her circle of friends forward.