However, it's worth noting that the escape is a culmination of events from previous episodes, and the actual escape takes place in the final scenes of the episode.
They were free. Or so they thought.
The plan was supposed to be flawless. It relied on the pipes, the psychotic John Abruzzi, the guard keys, and the medical ward. But in the weeks leading up to the finale, everything that could go wrong did. The pipe was replaced. The psychotic Abruzzi was replaced by a quiet inmate named "Psyche." The key didn't work. Michael was thrown into solitary confinement. what episode does scofield escape fox river