This is a prison facility with a basketball court, an electric chair room, main office, jail room with beds, some corridors, a locker room, a room with 'keep all hands in plain view at all times' written all over the room, and a strange painting.
Newbie finds that the helicopter has crashed at the top of the cursed "Alcatraz". He then jumps off the Bridge, after realizing that monsters were just behind him and manages to get into the crashed helicopter.
Walk through the strange painting in a cell and look around to find the coin, However on hard mode enemies spawn quickly in this area, so it is advised to kill all of them then get it on easy or medium mode.
The gem is on the second floor of the prison cell block, around the corner of where there's an exit outside.
Do not get too close, as the monsters will hit you.
Kill the monsters as quickly as possible, since you earn a star by killing monsters quickly. Do not rush it, though.
Use pets, as a minor/major backup for killing.
Follow the green arrow that appears once there are 5 enemies left, in order to kill the enemies quicker.
To conserve munitions, aim for the enemies' heads.
Use Armor. If you have a decent amount of armor, you will not have to worry about getting damaged, because you can get 3 stars even if you have ended with damaged armor. But this doesn't apply to Health.
The enemies aren't extremely tough in this level, so you can equip the weapons with a decent amount of damage.
It is recommended to not stay inside the prison, as you can be easily trapped by enemies or even the boss, and you can be easily damaged by them.
Dodge the attacks of the boss and avoiding contact with it.
It is unknown how the island got infected. Seeing how it's isolated from the mainland, and no flying monsters were present.
Although any flying transportations (like the helicopter in the story comic above for example) might have landed with a monster with it and have infected the people in the Prison. But the actual reason remains unknown.
It is based on the Alcatraz Island, namely the prison constructed on there.
In the loading screen. You will see a prisoner execution device: An Electric Chair. It is one due to the electric symbols found and its switch on the left side.
It was removed from multiplayer in the 10.6.0 update.