  Even over relatively recent epochs, galaxies have evolved significantly in
their location in the mass-metallicity plane, which must be telling us
something about the latter stages of galaxy evolution. In this paper, we
analyse data from the LEGA-C survey using semi-analytic spectral and
photometric fitting to determine these galaxies' evolution up to their observed
epoch at $z \sim 0.7$. We confirm that, at $z \sim 0.7$, many objects already
lie on the present-day mass-metallicity relation, but with a significant tail
of high-mass low-metallicity galaxies that is not seen in the nearby Universe.
Similar modelling of the evolution of galaxies in the nearby MaNGA survey
allows us to reconstruct their properties at $z \sim 0.7$. Once selection
criteria similar to those of LEGA-C are applied, we reassuringly find that the
MaNGA galaxies populate the mass-metallicity plane in the same way at $z \sim
0.7$. Matching the LEGA-C sample to their mass-metallicity "twins" in MaNGA at
this redshift, we can explore the likely subsequent evolution of individual
LEGA-C galaxies. Galaxies already on the present-day mass--metallicity relation
form few more stars and their disks fade, so they become smaller and more
bulge-like. By contrast, the high-mass low-metallicity galaxies grow their
disks through late star formation, and evolve rapidly to higher metallicities
due to a cut-off in their wind-driven mass loss. There are significant
indications that this late cut-off is associated with the belated end of strong
AGN activity in these objects.
