When a letter from Soup and Rob brings less-than-intrepid radio hero Sinker O. Sailor to Learning, Vermont, the whole town turns out for a picnic climaxed by Sinker's spectacular entrance, flying out of Suicide Flume aboard a daffy craft assembled by the boys from found materials. As usual, Peck pokes painless fun and his nonstop plot is festooned with puns, one-liners, double-entendres and alliteration — Rob laments that one of his friend's "culpable capers had taken root, and sprouted, soon to flower into some blooming butchery that would topple the two of us into a ton of trouble." True, but the lads still come out on top, with nemeses Janice Ryker and Eddy Tacker deservedly vanquished. A polished new entry for this popular series, slightly less contrived than Soup's Hoop (1990). Likably casual soft-pencil drawings. (Fiction. 9-11)