  We report on a large stellar flare from the nearby dMe flare star EV Lac
observed by the Swift and Konus-Wind satellites and the Liverpool Telescope. It
is the first large stellar flare from a dMe flare star to result in a Swift
trigger based on its hard X-ray intensity. Its peak f_X from 0.3--100 keV of
5.3x10^-8 erg/cm2/s is nearly 7000 times larger than the star's quiescent
coronal flux, and the change in magnitude in the white filter is >4.7. This
flare also caused a transient increase in EV Lac's bolometric luminosity
(L_bol) during the early stages of the flare, with a peak estimated L_X/L_bol
~3.1. We apply flare loop hydrodynamic modeling to the plasma parameter
temporal changes to derive a loop semi-length of l/Rstar =0.37 +/-0.07. The
soft X-ray spectrum of the flare reveals evidence of iron Kalpha emission at
6.4 keV. We model the Kalpha emission as fluorescence from the hot flare source
irradiating the photospheric iron, and derive loop heights of h/Rstar=0.1,
consistent within factors of a few with the heights inferred from hydrodynamic
modeling. The Kalpha emission feature shows variability on time scales of ~200
s which is difficult to interpret using the pure fluorescence hypothesis. We
examine Kalpha emission produced by collisional ionization from accelerated
particles, and find parameter values for the spectrum of accelerated particles
which can accommodate the increased amount of Kalpha flux and the lack of
observed nonthermal emission in the 20-50 keV spectral region.
