I Am Pilgrim by Terry Hayes Emily Bestler Books/Atria-Simon & Shuster, $26.99, 612 pages, ISBN 978-1-4391-7772-3 On occasion, a work of fiction comes along which can only be described as riveting. Enthralling, arresting, gripping, fascinating, absorbing, captivating, hypnotic, engrossing or spellbinding . . . but the single best and most descriptive word for MBR No. 181 is riveting. It will drill a hole into your consciousness, insert a red-hot