Escape Dead Island

During Chapter 10 - Faith, you'll be asked to search Emory Crown's residence.

While exploring, you'll come to a large, two story room that's divided in two by debris. The side you enter has 2 Phantom Zombies and ends at a door you can open. On the other side of the debris (to your right as you enter the door) you'll see a staircase leading up. You have to go through the door at the end on the side you start on to make your way over to that staircase. There are an additional 2 Phantom Zombies roaming that side with a Phantom Spitter to boot, so take care of them.

When you finally enter the room with the stairs, 3 more Phantom Zombies and a Phantom Spitter will spawn upstairs and will be immediately hostile to you. You can hide under the stairs (and grab the Charon CD) and they won't find you. Actually, though, whether you stealth this or not, you really should clear the room of enemies before grabbing the Shotgun Upgrade. More on that in a bit...

Before you start roaming around upstairs take note: there is a wide open door at the top of the stairs that says BIOHAZARD on it. Do not go into this room until you have cleared the other enemies. Once the area is clear, you can enter the BIOHAZARD room, but be warned, it will spawn a Phantom Butcher in the room and he will always be hostile to you. You're going to have to fight him.

Once he's dead, go back to the BIOHAZARD room and in the corner where the Phantom Butcher spawned there is an Upgrade Bench holding the Hellfire Shotgun upgrade.