Start running over to the left and then head for the archway you can see on the right. Go on through it for another cutscene where the Drawbridge is drawn up.
You need to find another way into the castle now. Turn to the left and start for the ladder you can see there:
Head straight from the room in front of you. Go out of the window on the far side of it. Turn to the left when you get there:
At the top of the ladder, continue over to the left. Take the next ladder there up as well. Turn to the wall to the left of the top of the ladder. Follow the onscreen prompt to start climbing upwards. Head straight into the doorway in front of you that gets filled with smoke.
Turn to the right and head down the staircase through the doorway. This will bring to where you are needed. Just head through the door to start your chase.