  The Gaia satellite has provided the community with three releases containing
astrometrical and photometric data as well as by products, such as stellar
parameters and variability indicators. By selecting in the Gaia database, one
can select stars with the requested characteristics, such as high speed. At
present any selection is based on available Gaia releases including a subset of
the observations. This, for some stars, can show some limitations, for example
there is still not a sufficient number of observations to detect binarity. We
investigated a star selected in Gaia EDR3 for its high speed that appears
unbound to the Galaxy. We requested high-quality spectra to derive more
information on the star. {From the spectroscopic investigation we confirm the
low metallicity content of the star, and we derive a detailed chemical
composition. The star is poor in carbon and very rich in oxygen:
[(C+N+O)/Fe]=+0.65. From the two spectra observed we conclude that the star is
in a binary system and from the investigation of the ionisation balance we
derive that the star is closer than implied by the Gaia DR3 parallax, and thus
has a a lower intrinsic luminosity. The star is probably still unbound, but
there is the possibility that it is bound to the Galaxy. Its low carbon
abundance suggests that the star was formed in a dwarf galaxy.
