Relax. The whole purpose of Marleybone is to find "Meowiarty's Hideout" Just to clarify he is in Big Ben, the final dungeon in Marleybone. It will be the last quest you will have to complete before preceding to MooShu.
Have you done Counterweights East and West? Those are required before you're allowed into Big Ben. You didn't say where you are in your timeline so I don't know how to help you. If you look on Wizard101 Central it's all explained with some pictures even. That helps a lot so you know what you're in for.
PLEASE ANYONE!!! im confused! I cant find meowiarty's hideout location it just says on my quest to find the location and.... i dont know im just so confused can anyone please give me a hand?? Sincerely, Stephine Swiftbreeze level 37 school of ice
After you talk to Watson, you will get further instructions. Follow them. You will not get to Big Ben without completing the main story line quests given you. (those are the ones you cannot decline, by the way)
Once you complete Katz's lab and get back to the museum you talk to Sherlock. He tells you to help so-and-so in Counterweights East. Finish that, go back to him and he tells you to do Counterweights West. Finish that, report back to Sherlock and he says great job. Now the guy next to him has a quest mark over his head. He's letting you into Big Ben. This instance takes a couple hours so plan your time to finish it. Make sure your mana bottles a full, but don't use one until you get to the next level and see who's there. As long as you don't move when you come out of the elevator you can look in your spell book and add treasure cards if you need them. Sometimes there are wisps waiting for you also. It took me 4 attempts the first time. Good luck.