This was the first issue of CHALLENGERS in two years when it came out, and reprints two stories from 1959, although changing the Challs jumpsuits from the original purple to a red/yellow combination.
First up, "The Isle of No Return", a 12-page Kirby/Wood story from CotU #7. Investigating a thief using advanced scientific devices. They follow him to an island (with June along as a stowaway), and find out that the thief has even more devices, stolen from a now dead reclusive scientist, including a device which shrinks the Challs.
Fortunately June is able to find them, and with some help from a pet parrot and the late scientist's own safeguards they manage to defeat him.
Next is "The Sorceress of Forbidden Valley", also Kirby/Wood, a 10-pager from CotU #6. This time June is flying through a storm and is forced to make a crash-landing on a mysterious island. The Challs go looking for her, and find her with magical powers and under the control of a criminal who had found a hidden city. Fortunately they're able to escape.
I don't think the half-issue stories for the Challengers are as good as the full issue stories, they all seem to end kind of abruptly, but they do give Kirby a good chance to draw various scenes, like a hidden city and a lab packed with scientific wonders.
The cover is also reprinted from CotU #7, with a few minor modifications, and the splash page is a reprint of the Kirby/Stein introduction to the team that appeared in CotU #1 (1958).