Am I stuck? Can't move forward from Batcave

[Dookus]

I finished chapter 3, Arkham Asylum Antics. When finished, it dumped me straight into the next chapter, Asylum Assignment, but I chose to return the batcave and quit for the night.

Now, I'm in the Batcave, and chapter 4 isn't on my map. Replaying Chapter 3 didn't help, because replay made doesn't proceed like the normal game - it returns you to the batcave.

So is the game over for me? Is there some way around this? Or am I missing something obvious?

 

[Dookus]

Aha! Never mind. I wandered around Gotham until I saw the beam of light in Arkham.

 

[stork]

Where's the beam of light in Arkham that allows you to proceed to level 4?