You would need to go to the computer containing the book.
Select the saved book in the Collection panel.
Go to Grid View [ G ] and select all the images [Cmd/Ctrl][A]
File>Export as Catalog and store on media you can use to transfer
Bring this catalog onto your computer
File>Import from another catalog and bring the transitory catalog into your master catalog.
It should bring the images, your collections (including your book) and other settings into your own catalog.
THE BOOK IS NOW ON MY BACKUP EXTERNAL HARD DRIVE. ARE THE INSTRUCTIONS THE SAME?