Sherlock, to be out of your depth

Sherlock, Series 01, Episode 01, A Study in Pink


Dr John Watson: Who are you? What do you do? 
Sherlock Holmes: What do you think? 
Dr John Watson: I'd say private detective... 
Sherlock Holmes: But? 
Dr John Watson: But the police don't consult private detectives. 
Sherlock Holmes: I'm a consulting detective. The only one in the world - I invented the job. 
Dr John Watson: What does that mean? 
Sherlock Holmes: It means when the police are out of their depth - which is always - they consult me. 


to be out of your depth: to be involved in a situation or activity which is difficult for you to understand or deal with