  M31N 2008-12a is a remarkable recurrent nova within the Andromeda Galaxy.
With eleven eruptions now identified, including eight in the past eight years,
the system exhibits a recurrence period of one year, and possibly just six
months. This short inter eruption period is driven by the combination of a high
mass white dwarf ($1.38\,\mathrm{M}_\odot$) and high mass accretion rate
($\sim1.6\times10^{-7}\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$). Such a high
accretion rate appears to be provided by the stellar wind of a red giant
companion. Deep H$\alpha$ observations have revealed the presence of a vastly
extended nebula around the system, which could be the `super-remnant' of many
thousands of past eruptions. With a prediction of the white dwarf reaching the
Chandrasekhar mass in less than a mega-year, M31N 2008-12a has become the
leading pre-explosion type Ia supernova candidate. The 2016 eruption - to be
the twelfth detected eruption - is expected imminently, and a vast array of
follow-up observations are already planned.
