  Nova Per 2018 (= V392 Per) halted the decline from maximum when it was 2mag
brighter than quiescence and since 2019 has been stable at such a plateau. The
ejecta have already fully diluted into the interstellar space. We obtained
BVRIgrizY photometry and optical spectroscopy of V392 Per during the plateau
phase and compared it with equivalent data gathered prior to the nova outburst.
We find the companion star to be a G9 IV/III and the orbital period to be
3.4118 days, making V392 Per the longest known period for a classical nova. The
location of V392 Per on the theoretical isochrones is intermediate between that
of classical novae and novae erupting within symbiotic binaries, in a sense
bridging the gap. The reddening is derived to be E(B-V)=0.72 and the fitting to
isochrones returns a 3.6 Gyr age for the system and 1.35 Msun, 5.3 Rsun, and 15
Lsun for the companion. The huge Ne overabundance in the ejecta and the very
fast decline from nova maximum both point to a massive white dwarf (M(WD) >=
1.1-1.2 Msun). The system is viewed close to pole-on conditions and the current
plateau phase is caused by irradiation of the CS by the WD still burning at the
surface.
