  We present simultaneous ASCA and RXTE observations of Ark 564, the brightest
known ``narrow-line'' Seyfert 1 in the 2-10 keV band. The measured X-ray
spectrum is dominated by a steep (Gamma~2.7) power-law continuum extending to
at least 20 keV, with imprinted Fe K-line and -edge features and an additional
``soft excess'' below ~1.5 keV. The energy of the iron K-edge indicates the
presence of highly ionised material, which we identify in terms of reflection
from a strongly irradiated accretion disc. The high reflectivity of this
putative disc, together with its strong intrinsic O VIII Ly-alpha and O VIII
recombination emission, can also explain much of the observed soft excess flux.
Furthermore, the same spectral model also provides a reasonable match to the
very steep 0.1-2 keV spectrum deduced from ROSAT data. The source is much more
rapidly variable than ``normal'' Seyfert 1s of comparable luminosity,
increasing by a factor of ~50% in 1.6 hours, with no measurable lag between the
0.5-2 keV and 3-12 keV bands, consistent with much of the soft excess flux
arising from reprocessing of the primary power-law component in the inner
region of the accretion disc. We note, finally, that if the unusually steep
power-law component is a result of Compton cooling of a disc corona by an
intense soft photon flux, then the implication is that the bulk of these soft
photons lie in the unobserved extreme ultraviolet.
