  We present new ALMA CO(2-1) observations tracing $2.2 \times 10^{10}$ solar
masses of molecular gas in Abell 2390's brightest cluster galaxy, where half
the gas is located in a one-sided plume extending 15 kpc out from the galaxy
centre. This molecular gas has a smooth and positive velocity gradient, and is
receding 250 km/s faster at its farthest point than at the galaxy centre. To
constrain the plume's origin, we analyse our new observations alongside
existing X-ray, optical and radio data. We consider the possibility that the
plume is a jet-driven outflow with lifting aided by jet inflated X-ray bubbles,
is a trail of gas stripped from the main galaxy by ram pressure, or is formed
of more recently cooled and infalling gas. The galaxy's star formation and gas
cooling rate suggest the lifespan of its molecular gas may be low compared with
the plume's age -- which would favour a recently cooled plume. Molecular gas in
close proximity to the active galactic nucleus is also indicated by 250 km/s
wide CO(2-1) absorption against the radio core, as well as previously detected
CO(1-0) and HI absorption. This absorption is optically thick and has a line of
sight velocity towards the galaxy centre of 200 km/s. We discuss simple models
to explain its origin.
