This section of Call of Cthulhu guide describes Chapter 11 called "Darkwater police station". You return here after the events shown in chapter 10 when Sarah Hawkins and Drake Algernon cast Shambler out for good.
In the cell
This chapter begins in a prison that the main protagonist is still in. After a while, two policemen will come, however, they will leave jail pretty fast and leave you alone in the cell. You cannot get out, so turn around and lie down on the bench to push the story forward.
After a while, Leviathan will come again. When talking to him, you will have to choose from 6 R'lyehian answers. Then the cell doors will open and you will be able to leave.
Go leftwards and look inside each cell to see sequences with main characters. After a while, you will reach the main protagonist's office door, and a short cutscene will be initiated that will take you to another location.
Examine the corpse
Now you get to play as Cat. After a short cutscene, you will encounter two thugs that caused the death of officer Henry West. Now, Cat has to interrogate them. You can choose any dialogue options, however, there is an opportunity to unlock The Rats in the Walls achievement by selecting the bottom options (Punch the one on the left or Punch the one on the right).
After selecting any of the dialogue options, you will receive a new task to examine the corpse in the warehouse. Enter the building and go towards the door to the left, upstairs - you need to go around the entire warehouse.
Upon getting there, activate the reconstruction. Examine Henry West's body. Now, leave the room and examine the blood stain nearby. Next, check the trace on the ground, by the warehouse entrance. Then examine the gun on the ground, the cultist, and the pack of cigarettes on the bench, by the perforated boat. Finish the reconstruction by examining one of the cultists.
Go back to Murphy
Upon regaining control over your character, you will receive a firearm. This, to be delicate, is not well polished in the game - you can easily miss while shooting at an enemy right in front of you. Nonetheless, you can use it to defend yourself. Leave the room, kill two enemies headed your way, and then leave the warehouse. This will activate a cutscene and end this short chapter.