  We present optical spectroscopy and multi colour photometry of the old nova
V840 Oph. We rediscovered the nova based on its position in the colour--colour
diagrams. It stands out as a very blue object with an additional red component.
We present the first optical spectroscopy of this candidate and confirm its
nova character. Furthermore, V840\,Oph has been found as one of very few
cataclysmic variables showing C IV emission at lambda = 580/1 nm. From the
analysis of the carbon lines it seems probable that V840 Oph contains actually
a carbon-rich secondary star. So far, only the nova-like QU Car has been known
to have such a companion. We furthermore find spectroscopic evidence that V840
Oph has a hot, dense accretion disc or stream and is probably a magnetic
system.
