  The observation by the Swift X-ray Telescope of the Fe K alpha_1, alpha_2
doublet during a large flare on the RS CVn binary system II Peg represents one
of only two firm detections to date of photospheric Fe K alpha from a star
other than our Sun. We present models of the Fe K alpha equivalent widths
reported in the literature for the II Peg observations and show that they are
most probably due to fluorescence following inner shell photoionisation of
quasi-neutral Fe by the flare X-rays. Our models constrain the maximum height
of flare the to 0.15 R_* assuming solar abundances for the photospheric
material, and 0.1 R_* and 0.06 R_* assuming depleted photospheric abundances
([M/H]=-0.2 and [M/H]=-0.4, respectively). Accounting for an extended loop
geometry has the effect of increasing the estimated flare heights by a factor
of ~3. These predictions are consistent with those derived using results of
flaring loop models, which are also used to estimate the flaring loop
properties and energetics. From loop models we estimate a flare loop height of
0.13 R_*, plasma density of ~4 * 10^12 cm^-3 and emitting volume of ~6 * 10^30
cm^3. Our estimates for the flare dimensions and density allow us to estimate
the conductive energy losses to E_cond <= 2 * 10^36 erg, consistent with upper
limits previously obtained in the literature. Finally, we estimate the average
energy output of this large flare to be ~10^33 erg sec^-1, or 1/10th of the
stellar bolometric luminosity.
