Phlogiston

Particles that form the flame.
Genius Society #2 Harald Punch proved its existence, but #3 Nyul Iman disproved it.
#7 Bohdan overthrew Iman's conclusion and proved it again before getting killed by #4 Polka Kakamond days after announcing Phlogiston's existence.

"Does it exist or not? We're not interested, frankly speaking."