An exceptionally good concept which should be copied by writers with slighly richer lives as children. Some of the old schoolmates he contacts seem genuinely confused regarding his purpose, while others don't get a full treatment as human beings it seems.
Finally, the fact that the book may have started off as an elaborate revenge for a practical joke 14 years before -- a very funny one which Danny still can't seem to find funny -- is rather thinly disguised.