The goal is to determine the composition of Plutos atmosphere and to constrain the nature of surface-atmosphere interactions. We perform high--resolution spectroscopic observations in the 2.33--2.36 $mu$m range, using CRIRES at the VLT. We obtain (i) the first detection of gaseous methane in this spectral range, through lines of the $ u_3$ + $ u_4$ and $ u_1$ + $ u_4$ bands (ii) strong evidence (6-$sigma$ confidence) for gaseous CO in Pluto. For an isothermal atmosphere at 90 K, the CH$_4$ and CO column densities are 0.75 and 0.07 cm-am, within factors of 2 and 3, respectively. Using a physically--based thermal structure model of Plutos atmosphere also satisfying constraints from stellar occultations, we infer CH$_4$ and CO mixing ratios q$_{CH_4}$= 0.6$^{+0.6}_{-0.3}$% (consistent with results from the 1.66 $mu$m range) and q$_{CO}$ = 0.5$^{+1}_{-0.25}$$times10^{-3}$. The CO atmospheric abundance is consistent with its surface abundance. As for Triton, it is probably controlled by a thin, CO-rich, detailed balancing layer resulting from seasonal transport and/or atmospheric escape.
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