  We study the propagation of scalar fields on various backgrounds in three
dimensional higher spin gravity. Our main emphasis is on obtaining the
bulk-boundary propagator, which can be efficiently computed using group theory
and higher spin gauge symmetry and from which we can extract scalar two-point
functions in the dual CFT. As an illustration, we obtain a simple closed form
expression for the propagator in a particular spin-3 deformation of AdS_3. In
the case of higher spin black holes, we prove on general grounds that the
propagator respects an imaginary time periodicity consistent with the thermal
nature of the black hole; in doing so we make progress in understanding the
group exponentiation of the higher spin Lie algebra hs[\lambda], and its
center. We also explicitly compute the propagator in the black hole background
at first order in the higher spin charge. Evaluated on the Lorentzian section,
the result is consistent with an interpretation in which the black hole has two
causally disconnected boundary components, as is the case for the BTZ black
hole.
