| Issue | #S-25 |
| Published | July-August 1971 |
| Cover Price | 0.25 USD |
| Pages | 68 |
| Editing | Murray Boltinoff |
| Characters | Challengers of the Unknown [Red Ryan; Ace Morgan; Prof Haley; Rocky Davis]; Tartan; Drabny; Darius Tiko |
| Genre | adventure |
| Pencils | Jack Kirby |
| Inks | Vince Colletta |
| Characters | Challengers of the Unknown [Ace Morgan; Rocky Davis; Prof Haley; Red Ryan]; June Robbins; Drabny (villain) |
| Synopsis | June's friend Marie comes to meet the Challengers to ask them to investigate weird events in her home country of Mordania. There they meet and fight the evil Drabny, whose scientific inventions have enabled him to take over Mordania. |
| Genre | adventure |
| Script | Jack Kirby; Dave Wood |
| Pencils | Jack Kirby |
| Inks | Wally Wood |
| Editing | Jack Schiff (Original Editor) |
| Reprinted | from Challengers of the Unknown (DC, 1958 series) #8 (June-July 1959) |
| Characters | Challengers of the Unknown [Ace Morgan; Prof Haley; Red Ryan; Rocky Davis] |
| Pencils | Bob Brown |
| Inks | Bob Brown |
| Characters | Challengers of the Unknown [Red Ryan; Ace Morgan; Prof Haley; Rocky Davis]; Tartan (villain) |
| Synopsis | The Challengers are abducted into space and forced to perform in a circus act under the control of the ringmaster Tartan. |
| Genre | adventure |
| Script | Jack Kirby; Dave Wood |
| Pencils | Jack Kirby |
| Inks | Wally Wood |
| Editing | Whitney Ellsworth (Original Editor) |
| Reprinted | from Challengers of the Unknown (DC, 1958 series) #6 (February-March 1959) |
| Synopsis | autobiography |
| Script | Jack Kirby |
| Characters | Challengers of the Unknown [Ace Morgan; Rocky Davis; Prof Haley; Red Ryan]; Harlan Fuller; Darius Tiko |
| Synopsis | The Challengers investigate a Greek soldier from ancient times who has been transported into the present and discover scientist Darius Tiko, who claims to have mastered time travel. |
| Genre | adventure |
| Script | Jack Kirby |
| Pencils | Jack Kirby |
| Inks | Wally Wood; Roz Kirby |
| Editing | Whitney Ellsworth (Original Editor) |
| Reprinted | from Challengers of the Unknown (DC, 1958 series) #4 (October-November 1958) |
| Characters | Challengers of the Unknown [Ace Morgan; Rocky Davis; Prof Haley; Red Ryan] |
| Synopsis | Tiko has sent the Challengers to ancient Greece. |
| Genre | adventure |
| Script | Jack Kirby |
| Pencils | Jack Kirby |
| Inks | Wally Wood; Roz Kirby |
| Editing | Whitney Ellsworth (Original Editor) |
| Reprinted | from Challengers of the Unknown (DC, 1958 series) #4 (October-November 1958) |
| Characters | Challengers of the Unknown [Ace Morgan; Rocky Davis; Prof Haley; Red Ryan]; Nostradamus |
| Synopsis | The Challengers are transported to ancient Egypt, then to the fifteenth century to meet Nostradamus, where they think he may be able to help them. |
| Genre | adventure |
| Script | Jack Kirby |
| Pencils | Jack Kirby |
| Inks | Wally Wood; Roz Kirby |
| Editing | Whitney Ellsworth (Original Editor) |
| Reprinted | from Challengers of the Unknown (DC, 1958 series) #4 (October-November 1958) |
| Characters | Challengers of the Unknown [Ace Morgan; Prof Haley; Rocky Davis; Red Ryan]; Darius Tiko |
| Synopsis | The Challengers pursue Darius Tiko to the year 3000, where the local law enforcement helps them defeat him. |
| Genre | adventure |
| Script | Jack Kirby |
| Pencils | Jack Kirby |
| Inks | Wally Wood; Roz Kirby |
| Editing | Whitney Ellsworth (Original Editor) |
| Reprinted | from Challengers of the Unknown (DC, 1958 series) #4 (September-October 1958) |
| Genre | adventure |
| Letters | typeset |
| Notes | Original story was not a Challengers story; reprint has been edited to replace non-Challengers characters with Ace and Prof. |
| Reprinted | from Challengers of the Unknown (DC, 1958 series) #15 (August-September 1960) |