Full story
Steven Grant is a shy gift-shop employee at a London museum. He sleeps tied to his bed because he keeps waking up in strange places, losing whole days without knowing why. One day he comes to in the Austrian Alps, holding a golden scarab, with armed men on his tail. There he meets Arthur Harrow, a charismatic cult leader with scales tattooed on his arm. And he starts hearing a deep voice calling him: Khonshu, the Egyptian god of the moon.
Bit by bit, Steven learns he shares his body with Marc Spector, an American ex-mercenary who serves as Khonshu's avatar, Moon Knight. When Marc takes over, Steven blacks out. Layla El-Faouly, an archaeologist, shows up demanding answers: she's Marc's wife. Harrow, a former avatar of Khonshu, wants to free the goddess Ammit, who judges people for what they will do and wipes out the guilty before the crime. The scarab is the map to her tomb.
The hunt moves to Egypt. Steven also learns to wear a suit of his own, Mr. Knight. Khonshu defies the other gods and ends up trapped in a stone figurine. Marc, Steven and Layla find Ammit's tomb inside the tomb of Alexander the Great, but Harrow gets there first and takes the goddess's figurine. He shoots Marc, who falls into the water.
Marc wakes up in a psychiatric hospital where Harrow is the doctor. In truth, he and Steven are in the Duat, the Egyptian afterlife, on a boat guided by the goddess Taweret. To balance the scales of their hearts, they relive memories. Steven learns the truth: Marc created him as a boy to escape the guilt over his brother Randall's death and the abuse from their mother, who recently died. Steven is lost to the sands, Marc goes back to save him, and the two earn the right to return to life.
In Cairo, Harrow frees Ammit. Layla agrees to be Taweret's temporary avatar and gains powers. Khonshu and Ammit fight as giants, and Marc and Steven, finally in sync, beat Harrow and seal Ammit inside his body. Marc refuses to kill Harrow and demands to be released from Khonshu. In the post-credits scene, a third identity surfaces, Jake Lockley, still serving Khonshu, and he kills Harrow. That comes back later.