### Clue: Acid lake busy dissolving American spy (6)
### Answer: PHILBY 
 ### Explanation: Acid lake busy dissolving American spy (6)
**PH1** ("acid") +** L** (lake) + **B**(us)**Y** [*dissolving* US] 
*Kim Philby was a British agent (one of the Cambridge Five) who was also an KGB agent.