We uncover a cascade of exceptional points (EPs) in the quasinormal mode spectrum of massive scalar perturbations of Kerr black holes, revealing an intricate non-Hermitian structure underlying their linear response. The cascade originates from a single damped mode that enters the extremal spectrum for sufficiently large field masses. We obtain evidence for an infinite sequence of EPs in the $(\ell ,m)=(1,1)$ and (2, 2) sectors near the extremal limit, mediating the transition between damped and zero-damping modes. Each EP carries a geometric phase that enables adiabatic mode mixing across the entire overtone spectrum, a phenomenon we refer to as adiabatic ergodicity.

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• Classical black holes
• Gravitation
• Exceptional points