FACE DOWN BEFORE THE REBEL HOOVES, by Kathy Lynn Emerson, St. Martin’s Minotaur, 256 pages, hardcover, $23.95.

Until the northern countesses began plotting rebellion, Susanna Appleton had left the political intrigue to her late husband Robert and his friends. Yet, when Robert’s former mistress is struck down and killed by a runaway horse, Lady Appleton becomes a spy to uncover and help undermine a plot to overthrow Queen Elizabeth I and place Mary Queen of Scots on the throne.

“Face Down Before the Rebel Hooves” is the sixth book by Wilton author Kathy Lynn Emerson to feature Elizabethan sleuth Susanna. It also is the first to involve the gentlewoman directly in one of the many documented schemes to topple the Virgin Queen from her throne. Previous novels have emphasized Susanna’s skills as an Elizabethan forensic scientist and expert herbalist as she’s unraveled murder plots.

Lady Appleton is in Hamburg with her lover Nick Baldwin, a successful merchant, as the novel opens in the fall of 1659. While Susanna is happier than she ever dreamed she could be with a man, she knows she must return to England before winter to attend to her Kent estate, Leigh Abbey, and to Rosamond, Robert’s daughter by his former mistress.

Her ruminations on how to break this news to Nick are interrupted by Robert’s friend and fellow spy, Sir Walter Pendennis. Walter’s wife and Rosamond’s mother, Eleanor, was the woman who was trampled by runaway horses, hence the title of the book. Walter brings Susanna sad and frightening news – Eleanor was a traitor.

Walter convinces Susanna to pretend to be Eleanor and carry to England a dispatch the woman had been given just before being struck down. This puts Susanna in the midst of Sir Thomas Percy of Northumberland’s plot to depose the Protestant queen and place the Roman Catholic queen of Scots on the English throne.

Percy and his followers seek to return the nation to the religion that Henry VIII, Elizabeth’s father, severed his people from when he sought a divorce from the pope so he could have a new wife capable of bearing sons. This plot was real and so were the women who pushed their husbands to execute it even when it became evident there was no possibility of success.

As Susanna unravels the characters and tries to determine who is behind the treason, she travels through northern England and into Scotland. Emerson’s description of the transportation travails the lady faces are harrowing. Women rode sidesaddle on horseback at the time. Their heavy clothes sometimes kept out the damp air, but once they became wet from rain or a river crossing, a lady could easily catch a life-threatening chill.

The accommodations in Susanna’s travels range from opulent castles even she finds outrageous to inns infested with rats to a simple peat-smelling cottage owned by Jock of the Side who demands that his exhausted visitors be gone within 24 hours. Manners of the day demanded that travelers be offered food and shelter, but such guests often were at the mercy of their hosts.

It is not Emerson’s plotting that makes her series so intriguing, it’s the rich and detailed descriptions of everyday Elizabethan life and her characters that keep readers hungry for more. By separating each book by two-year intervals, Emerson entices Lady Appleton’s fans to open the latest installment just to see how Susanna’s life and the lives of her extended family have developed.

“Face Down Before the Rebel Hooves” is the most satisfying book of the series. By thrusting her heroine into the midst of a historical, albeit minor, event, Emerson creates not just a mystery but an adventure that is impossible to put down.

A hint to readers new to this author: Read the historical note at the back of the book first and consult the cast of characters at the front of the book early and often.