Well, price appears to be part of the answer. Little, Brown dropped the e-book price of The Black Echo, the first title in Michael Connelly’s long-running Harry Bosch series, to $0.99 from $7.99 at the end of June. Over the past month, the e-book has become a bestseller.

Dan Lubart, principal of iobyte and eBook Market View, took a look at The Black Echo‘s rise for us. Before the promotion began, it was at #487 on the Nook bestseller list. It gradually climbed up the charts, then jumped from #128 on the Nook list on July 18 to #3 on July 19. It’s now at #2 on the Nook bestseller list. The Black Echo started out ranked over 100 on the Kindle bestseller list (Amazon (NSDQ: AMZN) only publishes its 100 bestselling Kindle titles) and is now at #2. The Black Echo is #13 on the Kobo bestseller list.

Little, Brown is a division of Hachette, one of the “big six” publishers that uses the agency model for e-books. The publishers set prices for e-books—which must be the same across all stores—and e-tailers get a cut. Agency publishers are just beginning to experiment with e-book sales—some participated in Amazon’s recent Big Deals promotion, for instance. The effect of a price drop on The Black Echo‘s sales rank should be good news for Hachette—and for other publishers of long-running series. They, like Hachette, can pull in new fans by putting the first book in a series on sale. Hopefully, readers will get hooked and buy the rest of the books in the series—that’s 16, in the case of Michael Connelly—at full price.

Check out our bestseller lists to find out the most popular digital content of the day from iTunes, YouTube (NSDQ: GOOG), Netflix (NSDQ: NFLX), Facebook, Kindle, Nook, Kobo, Last.fm, Android, and Hulu.