The Girl On The Train by Paula Hawkins Riverhead Books/Penguin Group (USA) LLC, $26.95, 325 pages, ISBN 978-1-59463-366-9 We’ve just returned from the annual Mountains and Plains Booksellers Association Trade Show in Denver, Colorado. It’s a yearly affair with 70 or 80 publishers, several hundred bookstore owners, their employees and managers. It features thousands of new books, authors, lectures and seminars about what’s hot, what’s not, trends in the