Heaven assigns the task to raise Biff, a childhood friend of Jesus Christ, from the dead to an angel named Raziel. Under Raziel's supervision, Biff must write his gospel to explain what Jesus, whose Hebrew name is Joshua, did before he started preaching. Biff's Hebrew name is Levi. Both the angel and Biff find the modern world confusing and frightening, but they both like pizza that they order from room service in their hotel. They share a single room and seldom leave. The man who delivers the pizza is ironically named Jesus.

Biff writes about his childhood experiences with Joshua and how Joshua does not know how to be the Messiah. All he can do at this stage is to resurrect lizards and people for a few moments. A rabbi suggests that the Magi who had visited during his birth may be able to help. Biff accompanies Joshua on his quest to visit the three Magi named Balthesar, Gaspar and Melchior. Balthesar, from his fortress near the town of Kabul in Persia, teaches Joshua ancient Chinese wisdom. Gaspar brings Joshua to the level of total Buddhist enlightenment, and Melchior directs the Messiah in the ways of doing miracles, such as multiplying food. Biff learns kung fu and how to make explosives. He also enjoys quite a few sexual adventures, but Joshua cannot partake due to his status as the Son of God.

The journey also involves high adventure. Biff releases a demon in Balthesar's fortress that ends the very old man's life. Joshua is the only man on earth who can put the demon where he belongs, and he does so just in the nick of time. He meets an abominable snowman in the mountains near Gaspar's monastery and becomes friends with the almost human beast. Biff and Joshua break up a celebration to Kali in India and save the lives of many Untouchable children.

The two boyhood friends, now young men, return to Israel, where Joshua begins his ministry. He preaches to the multitudes, heals the sick, transforms water into wine, walks on water and multiplies food. He soon develops a following, including those who had followed John the Baptist before Herod had John beheaded. Maggie (Mary Magdalene) tricks her husband into divorcing her and joins with Joshua and Biff. The Pharisees put Joshua through several inquisitions to prove him a blasphemer, but none of this affects Joshua until he goes to Jerusalem for Passover.

While at the Temple in Jerusalem, Joshua loses his temper and overturns the moneychangers' tables. This leads to his trial and crucifixion. Biff, losing control at Joshua's death, chases down Judas and murders him. He then steps off a cliff and commits suicide.

After Biff finishes his gospel, the angel releases him from the hotel room. Maggie, Biff's one true love, has been writing her own gospel with another angel in the hotel room across from Biff. Maggie and Biff walk arm-in-arm away from the angels to live their bonus lives together.