  The Gaia satellite has already provided the astronomical community with three
data releases, and the Radial Velocity Spectrometer (RVS) on board Gaia has
provided the radial velocity for 33 million stars. When deriving the radial
velocity from the RVS spectra, several stars are measured to have large values.
To verify the credibility of these measurements, we selected some bright stars
with the modulus of radial velocity in excess of 500\ to be observed with
SOPHIE at OHP and UVES at VLT. This paper is devoted to investigating the
chemical composition of the stars observed with UVES. We derived atmospheric
parameters using Gaia photometry and parallaxes, and we performed a chemical
analysis using the code. We find that the sample consists of metal-poor stars,
although none have extremely low metallicities. The abundance patterns match
what has been found in other samples of metal-poor stars selected irrespective
of their radial velocities. We highlight the presence of three stars with low
Cu and Zn abundances that are likely descendants of pair-instability
supernovae. Two stars are apparently younger than 1\,Ga, and their masses
exceed twice the turn-off mass of metal-poor populations. This makes it
unlikely that they are blue stragglers because it would imply they formed from
triple or multiple systems. We suggest instead that they are young metal-poor
stars accreted from a dwarf galaxy. Finally, we find that the star RVS721 is
associated with the Gjoll stream, which itself is associated with the Globular
Cluster NGC\,3201.
