Do you dance Mr Darcy?

If you've committed a crime and a detective gathers everyone involved in the room, especially if he's not actually a detective and is instead a novelist, puzzle-setter, psychic, fake psychic, dog, chess grandmaster, etc. ...

YOU SHOULD NOT CONFESS.

Every year, hundreds of people are put away by non-traditional "detectives" who have either inserted themselves into the case or are working with the police in a dubiously legal capacity as advisor. In 99% of these cases, the murderer gives a full confession even though the evidence against them is circumstantial at best and often requires a long just-so story which can only guess at motive.

If this happens to you, stay quiet, do not attempt to defend yourself or talk your way out of it, only say "I want a lawyer".

Now if you find yourself being investigated by a boy genius, magician's assistant, anthropologist, classics scholar, or philosopher, it's likely that refusing to talk to the police (or investigator with no legal authority) is merely the end of the second act, and by the end of the third act they will have you dead to rights.

YOU SHOULD STILL NOT CONFESS.

Make them take it to court. Force the eccentric detective and his straight-laced police partner to take the stand and explain their methods to a jury of your peers. Have your lawyer look at the chain of custody on the evidence, especially if you believe it to have been handled by someone who has only bumbled into detective work through their natural charm and/or unique set of skills and outsider perspective that come in handy more often than they should.