  We have discovered that the star S986 in the old open cluster M67 has
detectable total eclipses of depth 0.08 mag for the primary eclipse and 0.011
mag for the secondary eclipse (in I only). We confirm the detection of a third
star in spectra contributing 11.5% +/- 1.5% of the total light in V band. The
radial velocity of the third star indicates that it is a cluster member, but it
is unclear whether it is physically associated with the eclipsing binary. Using
spectroscopic and photometric data, we deconvolve the photometry of the three
stars, and find that the primary star in the eclipsing binary is significantly
hotter than the turnoff. The two most likely explanations are that the primary
star is in a rapid phase of evolution near core hydrogen exhaustion (associated
with the turnoff gap in M67's color-magnitude diagram), or that it is a blue
straggler created during a stellar collision earlier in the cluster's history.
Our detection of Li in the primary star tightly constrains possible formation
mechanisms in the blue straggler explanation. Because S986 is often used to
constrain tidal dissipation models, this may imply that the strength of tidal
effects is underestimated.
