The January book is The Moving Finger by Agatha Christie.

"The placid village of Lymstock seems the perfect place for Jerry Burton to recuperate from his accident under the care of his sister, Joanna. But soon a series of vicious poison-pen letters destroys the village's quiet charm, eventually causing one recipient to commit suicide. The vicar, the doctor, the servants—all are on the verge of accusing one another when help arrives from an unexpected quarter. The vicar's houseguest happens to be none other than Jane Marple."