  Archival XMM-Newton data on the nearby Seyfert galaxy NGC 4051, taken in
relatively high and low flux states, offer a unique opportunity to explore the
complexity of its X-ray spectrum. We find the hard X-ray band to be
significantly affected by reflection from cold matter, which can also explain a
non-varying, narrow Fe K fluorescent line. We interpret major differences
between the high and low flux hard X-ray spectra in terms of the varying
ionisation (opacity) of a substantial column of outflowing gas. An emission
line spectrum in the low flux state indicates an extended region of
photoionised gas. A high velocity, highly ionised outflow seen in the high
state spectrum can replenish the gas in the extended emission region over ~10^3
years, while having sufficient kinetic energy to contribute significantly to
the hard X-ray continuum.
