Appearing in "Panic Beneath the Earth!"
- Brotherhood of Evil Mutants
- Avengers (Only in flashback)
- J.C. Pennysworth
- New York City
- New Mexico
- Carlsbad Caverns (First appearance)
- Eye of Agamotto
- Cloak of Levitation
- Cauldron of the Cosmos (First appearance)
- Images of Ikonn
- Mjolnir (Only in flashback)
- Captain America's Shield (Only in flashback)
- Captain America's Uniform (Only in flashback)
Synopsis for "Panic Beneath the Earth!"
As Nighthawk settles into the ranks of the Defenders with a new costume, Valkyrie once more expresses her desire to leave the team to sort out her identity crisis. However, things are cut short when they are contacted by Professor Xavier, who is seeking aid to stop Magneto's most recent plot.
Traveling with Xavier to Magneto's hidden lair, the group ends up fighting his Brotherhood of Evil Mutants and are captured. Breaking free, and fighting the Brotherhood again, they are too late to stop Magneto from awakening his most recent creation: Alpha, the Ultimate Mutant.
- Cover art: modifications by Romita.
- This issue debuts a new color scheme for Nighthawk's costume that contains a detachable jet pack.
- This issue contains a letters page, Defenders Dialogue. Letters are published from Mark Del Vecchio, Brian Richards, Ed Farbarik, Mike Cruden, and Michael Verderosa. The letters page also contains a Series "A' Value Stamp #8 Captain America.
- The X-Men's secret mission mentioned by Professor X is their investigation of Krakoa just before Giant-Size X-Men #1.