You’re bored so you just have to wander around for a bit.
Walk north towards the purple building in the back, The 1st Reality Bank, then to the right to see the front of the building. Walk south across the street to find more retail and walk to the right in front of the theater. You’ll reach the Parkview Restaurant on the corner. Walk into the alley to the right of the building.
The large yellow building is a second hand bookshop. Use the doors to go inside. Walk up the stairs on the left and walk to the right as far as you can go. In front of you is the occult-section. Use it to find a note that the book you’re looking for is being repaired.
Walk downstairs again and talk to the clerk behind the desk. Ask him about the book you want. He’s working on it but you can have a look so he’ll give you the BOOK. Use the book on yourself to have a look inside. You’ll see how Slocombe created a portal to hell.
To stop the attack on Reality, you need to act quickly but you can’t do it alone. You need to find some collaborators first. As precaution you’ll activate your STITCH ability to destroy outer planar beings.
Walk into the mayor’s office on the left and find the mayor. Next to him is the Adumbration you saw passing earlier. Use the stitch from your inventory on the Adumbration to clear it. You’ll hear a scream outside and when you look you’ll find Elandra clearing the Adumbration. Talk to Elandra and she’ll agree to help you. Together you’ll fight the First.
Game source: A copy of the game was found here on the internet.