  We present the first successful application of the method of Matched
Expansions for the calculation of the self-force on a point particle in a
curved spacetime. We investigate the case of a scalar charge in the Nariai
spacetime, which serves as a toy model for a point mass moving in the
Schwarzschild black hole background. We discuss the singularity structure of
the Green function beyond the normal neighbourhood and the interesting effect
of caustics on null wave propagation.
