  We present a high-resolution spectroscopic analysis of the
extremely-metal-poor star CS 22957-027, which Beers et al (1992) noted to
exhibit a rather strong G-band. For Teff = 4839 K, derived from broadband
photometry, our analysis obtains log g = 2.25, and a very low metallicity of
[Fe/H]=-3.43 +/- 0.12. The carbon-to-iron ratio is found to be enhanced by
about 2 dex relative to the solar value, similar to the handful of other
carbon-rich metal-deficient stars discussed by Norris et al (1997a) and Barbuy
et al (1997). From the 12C13C (1,0) Swan bandhead and 13CH lines the isotope
ratio 12C/13C is about 10, indicating a 13C enrichment. Nitrogen is also found
to be enhanced by about 1 dex. The s-process elements Sr and Ba are,
surprisingly, found to be under-abundant relative to solar, with [Sr/Fe]=-0.91
and [Ba/Fe]=-0.93. The star's low luminosity requires that the chemical
enrichment arises from mass transfer from an evolved companion, rather than
self-polluting dredge-up processes. However, the s-process elements Sr and Ba
are unusually low, with a solar ratio to one another, at variance with what
found in the ``classical'' CH stars. Finally we note that a feature due to 13CH
is present in coincidence with the Th II 401.9129 nm resonance line. The blend
is of relevance for the nucleo-chronology use of the Th II line in these
extremely metal poor stars, when significant 13C is present.
