Baker Street Irregular

noun2

1. •
   A casual assistant, especially in the context of detection or solving crime.

   • 'And I don't understand your position at all. It seems quite irregular.' 'So it is, madam. I may be called a Baker Street Irregular. […]' — 2010
2. •
   A fan of Sherlock Holmes stories.

   • On this night, in 1934 New York, a few enthusiasts met to celebrate the birthday of the man they most respected, admired and loved. The Baker Street Irregulars were officially born. — 2021