Possible Clues:

• Fell-sounding alter ego
• Preston handed them a record twenty-six - nil hiding, but not in a London Park!
• A park in London
• Dr. Jekyll's alter ego
• "Dr. Jekyll and Mr. ___"
• Dr. Jekyll and Mr. ___
• Steven-son villain
• Stevenson's brute
• Mr. of 19th-century fiction
• Henry of the House Judiciary Committee