Paleobiologist Emma Russell works for crypto-zoological organization Monarch, tracking down and studying Titans, giant monsters that once dominated the Earth. She and her daughter Madison witness the birth of a giant larva dubbed Mothra. Emma calms Mothra down with a device, the “ORCA”, which is capable of emitting frequencies that can attract or alter the behavior of Titans. An organization of eco-terrorists, led by Alan Jonah, attacks and kidnaps both Emma and Madison. Mothra manages to escape and cocoon herself underneath a waterfall.

Monarch scientists and soldiers led by Drs. Ishirō Serizawa and Vivienne Graham approach Mark, Emma’s ex-husband, to track down Emma and Madison. Mark is initially reluctant, due to his hatred for Godzilla after his son Andrew was killed during the 2014 attack on San Francisco. They follow Godzilla to Antarctica and realise Jonah intends to free a Titan encased in ice called “Monster Zero”. Jonah’s team ambushes the Monarch soldiers and Mark is unable to rescue Emma and Madison. Emma reveals to Mark that she was in allegiance with the terrorists the entire time, and frees and awakens Monster Zero, who kills Graham and several Monarch soldiers before flying off after engaging Godzilla in a fight.