  The properties of the interacting, eccentric orbit binary V1507 Cyg
(HD187399) are examined with spectra that cover wavelengths from 0.63 to
0.68um. The spectrum of the brightest star is very similar to that of the B8 I
star Beta Ori, although with absorption lines that show sub-structure
consistent with a varying tidal field. The bulk of the Halpha emission in the
spectrum appears to be associated with the brighter star. Evidence is presented
that the period of the system has been stable over timescales of many decades,
arguing against large-scale mass transfer at the current epoch. Absorption and
emission lines are identified that originate in an expanding asymmetric
envelope around the companion, and component masses of 6.4 +/- 0.9 and 14.0 +/-
0.9 solar are found, where the former applies to the brighter star and an
inclination of 46 degrees has been assumed. The evolutionary state of V1507 Cyg
is then that of a system in which mass transfer has progressed to the point
where the mass ratio has been reversed, with the brighter star stripped of much
of its initial mass. It is argued that the brighter star is an Alpha Cyg
variable, and that it is those light variations that dominate the system light
curve. V1507 Cyg is observed at or near the center of a diffuse HI bubble that
is detected at 408 and 1420MHz. It is suggested that the eccentric orbit is the
result of evolution in a hierarchical system.
