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Three years. He had been missing for three years. One disagreement with his Father, and argument with his best-friend, and he had disappeared.
When a new face arrives in Gotham, a mercenary, hunting for a Doctor, they get the first clue in finding him.
But when the Batfamily do find their missing member, it's clear he has changed, he's got new friends, new beliefs, and a new name: Prometheus.