["The Island Stallion"] is the first of a series of stories about wild horses in a lost valley on a little-known Caribbean island. That is enough to make most young people reach for it, and they won't put it back on the shelf until they have heard the last hoofbeat. (p. 40)
Steve's adventures with Flame, and what Pitch found in the subterranean Spanish fortress make exciting reading.
A story like this is necessarily improbable. Parts of this one—for example the derrick that worked perfectly after standing idle for three hundred years—are fantastic; but the story sweeps along so rapidly that young people will not stop to question its plausibility. There are hours of good entertainment here. Readers will probably wait eagerly for the sequel. (p. 42)
Merritt P. Allen, "Books for Young People: 'The Island Stallion'," in The Saturday Review of Literature (copyright © 1948 by Saturday Review; all rights reserved; reprinted by permission), Vol. XXXI, No. 46, November 13, 1948, pp. 40, 42.