Three months ago, an underground nuclear test was conducted by the US Department of Defense in Arizona, but yields some unforeseen side-effects. The radiation from the test is channeled into an underground rift, a subterranean passage stretching from Arizona to Alberta, Canada. In Alberta, the radiation comes to fill an ice cave, within which a yeti-like creature is encased in a glacial tomb. The Sasquatch is freed from the ice by the radioactivity and revived. The newly revived monster is pained by the continuing effects of the radiation on his body. His mind filled with rage, the monster turns south, towards where he instinctively senses the source of his affliction originates. As he travels south, however, the radiation begins to make the man-monster start to grow.
In the present time, the S.H.I.E.L.D. Helicarrier follows the trail of Godzilla from Las Vegas, Nevada to the Grand Canyon in Arizona. Gabe Jones has reservations about using S.H.I.E.L.D. artillery in the canyon, but Dugan scoffs, calling him a monster-lover. They finally locate Godzilla, but when they do, they also see the monster Yetrigar. Hurling a huge boulder at the S.H.I.E.L.D. Helicarrier, Yetrigar takes S.H.I.E.L.D. out of the action. On the bridge of the Helicarrier, Robbie Takiguchi sneaks past the scrambling S.H.I.E.L.D. agents and gains access to the Red Ronin battlesuit. He hopes to intervene on Godzilla's behalf in his battle against Yetrigar.
Yetrigar ambushes Godzilla at the rim of the Grand Canyon, causing both monsters to topple into it. The fall doesn't affect them, they continue clawing and biting at one another. Godzilla blasts Yetrigar with his flame breath, but Yetrigar deflects it with a giant boulder. Godzilla maintains the upper hand though as he batters Yetrigar with his tail, then chomps down on his arm. Yetrigar frees his arm then punches Godzilla across the snout. The battle soon escalates when Red Ronin arrives to prevent the monsters from killing each other.