Irregardless of murder

Miss Prentice is an English teacher who deplores the use of the non-word "irregardless." When one of her ex-students is found dead in the town library, Miss Prentice finds herself working with Gil Dickensen, her long-ago ex-fiance, to find the murderer. The rumor mill says that Marguerite's death was a self-induced drug overdose, but Miss Prentice can't believe that Marguerite was a drug user. But who would want to kill Marguerite and why?