The thing to do is to get into the Strand Theater and look around, but how?
5 seconds sound clip from Scooby-Doo, Where Are You! - The Backstage Rag (S1E9).
You can hear this line at 00:05:56.047 in the Blu-ray version of the episode.
Quote context
[...]
- You think the other dog was a puppet?
- So it was the girl dog puppet that lured you away from the violin case.
- It looks like we have ourselves a little mystery.
- Let's examine the clues. A puppet dog, a violin case, packs of brand-new bills... Very strange.
- They don't seem to hold together. Unless...
- That's it! Counterfeiters! Huh?
- The thing to do is to get into the Strand Theater and look around, but how?
- How about getting an audition for a trained dog act?
- Don't look now, fans, but I think a star is about to be born.
- A watchman or a doorman, most likely.
- Look. He's working a puppet.
[...]