In this chapter, Titus kills. A lot. He runs a bit, too.
Just when you've had about enough of running, some Renegade Militia will ambush you, so kill them. The last Militia you kill will turn into a Bloodletter Daemon. Kill it too, then move forwards and deal with the Tainted Psyker. Run forward towards the objective marker to hit a checkpoint.
Approach the objective marker and you'll have another Tainted Psyker fight on your hands. You know what to do. When the Daemon blood stops flowing, proceed forward.
Grab some ammo and keep moving. Move forward into some ruins and prepare to fight more Renegade Militia and Chaos Space Marines. Follow the objective marker and engage some more Renegades in close-quarters combat. Keep moving forward and hit a checkpoint.
Continue forward and you'll have yet another Daemon-heavy fight. Make your way downward and kill everyone. Once the entire army is dead, the force field will lift and allow you to continue. Go through it and hit a checkpoint.
Keep walking and kill some more Daemons. Don't quite turn right just yet, but walk forward and collect another Servo Skull (Under Attack 2/3). March on and continue your one-man massacre. Kill the Tainted Psyker and go up the stairs. Activate the lift on your left to end the chapter.