It is set in London in 15th century, and concerns the adventures of an apprentice of William Caxton, the printer.

The title refers to a load of paper with a unicorn watermark, ordered by Caxton from Flanders but never delivered.

Harnett and The Load of Unicorn were a commended runner up for the Carnegie Medal from the Library Association, recognising the year's best children's book by a British subject.

Caxton sends Bendy and another apprentice on a quest to find the complete manuscript of Thomas Mallory's stories of King Arthur.

The endpapers of the first and some later editions are printed with 15th-century maps of London, and the illustrations show many of the everyday objects of the time.