After Completing all 6 Missions you unlock a special Mission where you play as Jenny. Your sword is also swapped for a gun.
Follow the route I take to rescue all the prisoners.
1. When you reach the first long hang wire go all the way to the right before dropping down or you will miss a prisoner.
2. When you see a bomb next to a prisoner get to the bomb as quickly as possible to disarm it. You just have to walk over it to disarm it.
3. The achievement only unlocks at the end of the stage not after the last prisoner is saved.