### Clue: Mystery man to leave unemployed ranks during trip (3,4,2,4)
### Answer: THE SIGN OF FOUR 
 ### Explanation: Definition: Mystery
**HE** ("man") + **SIGN OFF** (the dole) ("leave unemployed ranks") *during* TOUR ("trip") 
The Sign of Four* by Conan Doyle was the second Sherlock Holmes novel.