The small man in the dark suit is a great disappointment to the Siberia Central School class that's been looking forward to having pretty Miss Kellogg for a whole year--Miss K. who bestows kisses and rides in her brother's plane. But class cutups Finley Streeter and Stanley Dragavich discover that Lester Little, for all his mild appearance, is no slouch either. He can take a joke (a copy of Horsy Harem tucked into his furled umbrella) and turn the tables. And he's not a tattle-tale: when the boys pull off their biggest, most embarrassing prank--decking the statue of the town heroine in his name-taped lavender (a case of the colors running) undershorts--he's the one who gets them out of the ensuing fix without giving them away. It's all pretty corny but not cruel or cheap--ending in a bit of wisdom that's worth reading for itself. Mr. L. has rescued Miss K.--returned to play that town heroine in a pageant--and become a hero himself. ""But,"" he reminds the boys, ""it takes so much more courage. . . to be a gentleman.