A book in iBooks won't finish downloading and I can neither open/read it nor delete it.

I had the same problem, and here’s what worked for me:

1. Open the Settings app and go to the iTunes & App Store section.
2. Sign out of your iTunes account
3. Open the iBooks app, and it should update your book listing, which will no longer show the book that was stuck downloading.
4. iBooks will prompt you to log in to sync bookmarks, etc. and to see your books in the cloud. Dismiss this dialog without signing in.
5. Go back to the Settings app and log in to your iTunes account.
6. Go back to iBooks, and after the book listing updates, the book that was stuck downloading should now appear available in the cloud. You can leave it there or try downloading it again.

I downloaded the book that was stuck and it worked for me this time. Hope it’s the same for you.

Someone with a similar problem previously solved it by deleting the entire iBooks app, rebooting and resyncing with iTunes multiple times. Unfortunately for me:

• neither "quitting" iBooks through the app switcher nor rebooting the iPad helped
• iBooks is bundled on iOS 8 so you can't delete it (sledgehammer approach but I was willing to do it)
• I've never synced this iPad with a computer before, don't think it will help and don't really want to start now (in the past with devices that rarely got synced I used to get really frustrated by random apps being transferred on sync, home screens being reorganised, and other strangeness introduced by iTunes)
• going into "Manage Usage" shows me how much space is being taken up by iBooks but doesn't let me clear that space

Anyone got any other ideas? Is there anyway to probe inside iCloud drive to find where this stuff gets stored and clear it out?

thank you Eliot. This worked perfectly for me.

Thank you so much!