We study a class of supersymmetric spinning particle models derived from the radial
quantization of stationary, spherically symmetric black holes of four dimensional N= 2
supergravities. By virtue of the c-map, these spinning particles move in quaternionic
Kaehler manifolds. Their spinning degrees of freedom describe mini-superspace-reduced
supergravity fermions. We quantize these models using BRST detour complex technology. The
construction of a nilpotent BRST charge is achieved by using local (worldline)
supersymmetry ghosts to generating special holonomy transformations. (An interesting
byproduct of the construction is a novel Dirac operator on the superghost extended Hilbert
space.) The resulting quantized models are gauge invariant field theories with fields
equaling sections of special quaternionic vector bundles. They underly and generalize the
quaternionic version of Dolbeault cohomology discovered by Baston. In fact, Baston's
complex is related to the BPS sector of the models we write down. Our results rely on a
calculus of operators on quaternionic Kaehler manifolds that follows from BRST machinery,
and although directly motivated by black hole physics, can be broadly applied to any model
relying on quaternionic geometry.