  Cataclysmic Variables (CVs) are semi-detached binaries composed of a white
dwarf orbiting a lower-mass K or M star. We investigate whether CVs are
responsible for a new intriguing feature (the `hook') that appears in the Gaia
DR3 colour-magnitude Hertzsprung-Russell diagram (HRD) when selecting sources
with low extinction. We also aim to understand the location of CVs in the HRD
based on the predictions of the disc instability model (DIM). The DIM is the
foundation on which rests our basic understanding of stable (novae-like) and
outbursting CVs (dwarf novae). We calculate the expected behaviour of CVs in
the Gaia HRD taking into account the variable light contributed by the
accretion disc, the companion, the white dwarf, and from the bright spot where
the Roche lobe overflow stream from the companion intersects the disc. We find
that the `hook' feature is most likely to be composed of CVs. The `hook'
corresponds to the limited region where stable CVs (novae-likes) must be
located in the HRD according to the DIM, with the bluest systems having the
shortest orbital period. Unstable systems, giving rise to dwarf novae
outbursts, trace counterclockwise loops in the HRD. The overall behaviour is
consistent with the location of the various CV subtypes in the HRD. These
results can be used as a basis to pinpoint interesting outliers in the HRD,
either due to their location or their tracks. These outliers may signal new
subtypes such as cold, stable CVs with truncated discs, or may challenge the
disc instability model.
