The Case of the Missing Mutants

In Defenders #124, Beast reminded Iceman an an early plot orchestrated by the Secret Empire.

Beast: Or have you forgotten how the Empire kidnapped you, me, and half the mutants in the Western Hemisphere a few years back--and tried to tap our X-energies for their own ever-so nasty ends?

Beast wasn't exaggerating. After the Irish mutant Banshee feared that he might be the next one abducted (Captain America #172), Professor X, Cyclops and Marvel Girl of the X-Men enlisted the help of Captain America and Falcon to rescue the following mutants from the clutches of the Secret Empire:

Angel Beast Blob Havok Iceman Mastermind Mesmero Unus Lorna Dane (not yet Polaris)

Concluding in Captain America #175 (April 1974), the suspenseful storyline explained the X-Men's absence at a time when their own title published only reprints. The number of known mutants from the Eastern and Western Hemispheres would increase drastically in the year ahead, with the return of all-new X-Men stories in their series.

These images come from Captain America #172 (above) and #175 (below).