  Nova Mon 2012 was the first classical nova to be detected as a high energy
$\gamma$-ray transient, by Fermi-LAT, before its optical discovery. We study a
time sequence of high resolution optical echelle spectra (Nordic Optical
Telescope) and contemporaneous NOT, STIS UV, and CHIRON echelle spectra (Nov
20/21/22). We use [O III] and H$\beta$ line fluxs to constrain the properties
of the ejecta. We derive the structure from the optical and UV line profiles
and compare our measured line fluxes for with predictions using Cloudy with
abundances from other ONe novae. Mon 2012 is confirmed as an ONe nova. We find
E(B-V)=0.85$\pm$0.05 and hydrogen column density $\approx 5\times 10^{21}$
cm$^{-2}$. The corrected continuum luminosity is nearly the same in the entire
observed energy range as V1974 Cyg, V382 Mon, and Nova LMC 2000 at the same
epoch after outburst. The distance, about 3.6 kpc, is quite similar to V1974
Cyg. The line profiles can be modeled using an axisymmetric bipolar geometry
for the ejecta with various inclinations of the axis to the line of sight, 60
\le i \le 80 degrees, an opening angle of \approx$70 deg, inner radius $\Delta
R/R(t)\approx 0.4$ for permitted lines and less filled for forbidden lines. The
filling factor $f\approx 0.1-0.3$ implying M(ejecta) $\leq 6\times
10^{-5}$M$_\odot$. The ONe novae appear to comprise a single physical class
with bipolar high mass ejecta, similarly enhanced abundances, and a common
spectroscopic evolution within a narrow range of luminosities. The detected
$\gamma$-ray emission may be a generic phenomenon, common to all ONe novae,
possibly to all classical novae, and connected with acceleration and emission
processes within the ejecta (abstract severely truncated).
