  21-cm HI4PI survey data are used to study the anomalous-velocity hydrogen gas
associated with high-velocity cloud Complex M. These high-sensitivity,
high-resolution, high-dynamic-range data show that many of the individual
features, including MI, MIIa, and MIIb, are components of a long, arched
filament that extends from about (l, b) = (105{\deg}, 53{\deg}) to (l, b) =
(196{\deg}, 55{\deg}). Maps at different velocities, results from Gaussian
analysis, and observations of associated high-energy emission make a compelling
case that the MI cloud and the arched filament are physically interacting. If
this is the case, we can use the distance to MI, 150 pc as reported by Schmelz
& Verschuur (2022), to set the distance to Complex M. The estimated mass of
Complex M is then about 120 solar masses and the energy implied using the
observed line-of-sight velocity, -85 km/s, is 8.4 x 10^48 ergs. Integrating
over 4{\pi} steradians, the total energy for a spherically symmetrical
explosion is estimated to be 1.9 x 10^50 ergs, well within the energy budget of
a typical supernova.
