Using sharp scissors, remove the entire spine. Remove the leather up to the crease, but do not cut the hinge, which may release the binding and destroy the book.
Clean up the line with a razor blade. Do not leave any ragged edges.
Scrape paper and glue residue from the spine with a book repair knife.
Coat the spine area with a liquid glue binder.
Cut a piece of cloth or leather tape 1 1/2 inches longer than the cover and 1 1/2 inches wider than the spine.
Remove the tape's backing and set it aside, with the glue side up.
Cut a strip of stiff paper or card stock as long and as wide as the spine.
Set the strip in the center of the adhesive tape and press firmly.
Cut lengthwise into the tape, 1/8 inch from the edge along the paper strip. This leaves a center strip able to fold in onto the paper. Do so on each side, reinforcing the paper and leaving two flaps on each end of the tape.
Center the spine of the book on the paper strip. The middle paper piece should fit exactly; if it doesn't, remove it before it sets and cut it to fit.
Flatten the longer strips along the outside of the front and back covers using the back side of the razor blade or a ruler.
Open the book and press each of the four remaining flaps into the inside cover using the back of the razor blade or the ruler.