As the flavortext suggests, solving this puzzle involves going to "mass bookstores"--the numbers are street addresses for bookstores on Mass Ave. For each bookstore, take the initials of the author of the book in the specified location. (Book titles and authors are not given because they are subject to change.)
84 a book to read between hacks MIT Coop at Stratton Student Center; book is between the two hacking books (ARA) 698 a book to read on top of the tall bookshelf immediately to the right of the door Rodney's (BI) 731 a book to read third with the door on my left Seven Stars (AN) 862 a book to read after reading about myths and before my eyesight fails Hopewell's; book is between a mythology book and a large print book (ST) 1156 a book to read after reading about colonialism and before playing with my pets Revolution Books; book is between a book on colonialism in the Philippines and "Fat Cats and Running Dogs: The Enron Stage of Capitalism" (OR) 1256 a book to read when I am feeling very low (and immediately to the left of the door) Harvard Bookstore (YT) 1400 a book to read between the big game and getting on the expressway Harvard Coop; book is between "The Beanpot: 50 Years of Thrills, Chills, and Spills" and "The Innovation Highway" (IM) 2211 a book to read when standing on the front porch looking into the foyer (but not off-hours, to avoid disturbing the occupants' sleep) Kate's Mystery Books (ES)The initials of the authors, read in order, spell ARABIAN STORYTIMES, a clue for the answer NIGHTS.
Many, many thanks to: Barbara Boynton at the MIT Coop (who photoshopped a book cover for us!!), Jay at Rodney's, Ward at Seven Stars, Ben and Mary Lou Mehrling at Hopewell's, the folks at Revolution Books, Carole Horne at the Harvard Bookstore, Karen Porter at the Harvard Coop, and Kate of Kate's Mystery Books.