  H1517+656 is an unusual source, even for a BL Lac object. It is one of the
most luminous BL Lacs known, with extreme emission properties at radio,
optical, and X-ray frequencies. Furthermore, in our WFPC2 snapshot survey we
discovered a series of peculiar arcs describing a 2.4 arcsec radius ring
surrounding the source. This paper describes follow-up observations with
additional WFPC2 bands and the STIS longpass filter, which have revealed this
structure to be the remnants of a very recent galaxy merger. Population
synthesis modelling has shown that regions of the arcs have stellar populations
with age < 20 Myrs. Additionally, the circularity of the arcs indicates that
the plane of the collision and hence accretion is very close to the plane of
the sky. Given that BL Lac jets are thought to be aligned with the line of
sight, this observation may provide a direct link between the transfer of
angular momentum in an interaction and the generation of a radio source.
