  We present near infrared spectroscopy of Nova Herculis 2021 (V1674 Her),
obtained over the first 70 days of its evolution. This fastest nova on record
displays a rich emission line spectrum, including strong coronal line emission
with complex structures. The hydrogen line fluxes, combined with a distance of
4.7 (+1.3 / -1.0) kpc, give an upper limit to the hydrogen ejected mass of 1.4
(+0.8 / -1.2) 10^{-3} solar masses. The coronal lines appeared at day 11.5, the
earliest onset yet observed for any classical nova, before there was an obvious
source of ionizing radiation. We argue that the gas cannot be photoionized, at
least in the earliest phase, and must be shocked. Its temperature is estimated
to be 10^{5.57 +/- 0.05} K on day 11.5. Tentative analysis indicates a solar
abundance of aluminum and an underabundance of calcium, relative to silicon,
with respect to solar values in the ejecta. Further, we show that the vexing
problem of whether collisional or photoionization is responsible for coronal
emission in classical novae can be resolved by correlating the temporal
sequence in which the X-ray supersoft phase and the near-infrared coronal line
emission appear.
