  We estimate the abundances of S and Fe in the high velocity cloud HVC
287.5+22.5+240, which has a velocity of +240 km/s with respect to the local
standard of rest and is in the Galactic direction l~287, b~23. The measurements
are based on UV absorption lines of these elements in the Hubble Space
Telescope spectrum of NGC 3783, a background Seyfert galaxy, as well as new H I
21-cm interferometric data taken with the Australia Telescope. We find
S/H=0.25+/-0.07 and Fe/H=0.033+/-0.006 solar, with S/Fe=7.6+/-2.2 times the
solar ratio. The S/H value provides an accurate measure of the chemical
enrichment level in the HVC, while the super-solar S/Fe ratio clearly indicates
the presence of dust, which depletes the gas-phase abundance of Fe. The
metallicity and depletion information obtained here, coupled with the velocity
and the position of the HVC in the sky, strongly suggest that the HVC
originated from the Magellanic Clouds. It is likely (though not necessary) that
the same process(es) that generated the Magellanic Stream is also responsible
for HVC 287.5+22.5+240.
