The Lost Legend of Finn

From Author Wars - https://authorwars.com/publications/the-lost-legend-of-finn-570375.html

Overview:

Title: The Lost Legend of Finn
Author: Mary Tannen
Year: 1983
ISBN-10: 0394852117
Publisher: Alfred A. Knopf
Pages: 144
Binding: Hardcover
Type: Novel
Title Reference: The Lost Legend of Finn
Notes: 1st ed. LCCN and OCLC: -- "144 p. : ill. ; 22 cm." -- also ISBN 0394952111 (lib. bdg.) Publ date from Amazon as of 2016-05-12 (lib. bdg. ISBN, no list price, Look Inside! a later edition)

Illustrated, but neither LC nor any WorldCat record as of 2016-05-12 identifies the illustrator. That implies self-illustrated but the 1st ed. of book 1 was published one earlier with "drawings by John Burgoyne".