  The Andromeda Galaxy recurrent nova M31N 2008-12a had been caught in eruption
eight times. The inter-eruption period of M31N 2008-12a is ~1 year, making it
the most rapidly recurring system known, and a strong single-degenerate Type Ia
Supernova progenitor candidate. Following the 2013 eruption, a campaign was
initiated to detect the predicted 2014 eruption and to then perform high
cadence optical photometric and spectroscopic monitoring using ground-based
telescopes, along with rapid UV and X-ray follow-up with the Swift satellite.
Here we report the results of a high cadence multicolour optical monitoring
campaign, the spectroscopic evolution, and the UV photometry. We also discuss
tantalising evidence of a potentially related, vastly-extended, nebulosity. The
2014 eruption was discovered, before optical maximum, on October 2, 2014. We
find that the optical properties of M31N 2008-12a evolve faster than all
Galactic recurrent novae known, and all its eruptions show remarkable
similarity both photometrically and spectroscopically. Optical spectra were
obtained as early as 0.26 days post maximum, and again confirm the nova nature
of the eruption. A significant deceleration of the inferred ejecta expansion
velocity is observed which may be caused by interaction of the ejecta with
surrounding material, possibly a red giant wind. We find a low ejected mass and
low ejection velocity, which are consistent with high mass-accretion rate, high
mass white dwarf, and short recurrence time models of novae. We encourage
additional observations, especially around the predicted time of the next
eruption, towards the end of 2015.
