They came to the Flowing Sands River, a torrent so wide no bridge could cross it and so deep no boat could survive it. And in its depths dwelled the Sand Demon, a creature of immense strength and desperate grief.

He had once been a celestial general, punished for a single mistake: dropping a crystal cup at the Peach Banquet. The Jade Emperor, in his fury, had cast him from Heaven and condemned him to feed on travelers in this desolate river. Every seventh day, flying swords would pierce his body a hundred times.

He was not a demon by nature. He was a fallen immortal, waiting for redemption.

Wukong fought him for three days, but neither could defeat the other. The demon underwater was as strong in his element as Wukong was on land.

It was Guanyin who resolved the standoff. She appeared above the river in a lotus of light.

"You seek atonement," she told the Sand Demon. "Then put down your weapon and take up a burden. Carry the monk across the river. Become his disciple. Protect him on the journey west."

The Sand Demon rose from the water, his fists unclenching. His name was Sha Wujing. And from that day forward, he was the fourth disciple—the calm center, the silent strength, the sand that fills the gaps between fire and water.

The pilgrims had found their final companion.