Johnny awoke on the TechnoCore's analog of Old Earth.
At some point later in his life, Johnny decided that he wanted to cease being a cybrid and become a man. He began making plans to travel to Hyperion to accomplish this, since he would need to be outside the dominion of the TechnoCore to avoid immediate backlash from the Core after "investing" in his cybrid. Hyperion was unique among the colonies in that it had an especially primitive datasphere and nearly no TechnoCore contact. Johnny also believed it to be of special importance due to the apparent connection between the original John Keats and the current colonists of Hyperion.
Instead, he was brought to a remote location on Madhya where he was attacked with an AIDS II virus, which rendered him incapacitated for about a minute. While a relatively minor incident for a human, for an AI such an event is equivalent to being murdered.
He hires Brawne Lamia to investigate.
Johnny determines that at the exact nanosecond his AI consciousness leaves the datumplane to become one with his cybrid there will be a vulnerability in the Core that can be exploited.