  We present ALMA band-7 observations of J2057-0030, a multi-component merger
system at $z$ $\sim$ 4.68 spanning at least 50 kpc in size, using the [CII]
$\lambda$157.74 $\mu$m line and underlying far-infrared (FIR) continuum. We
find two main components, the quasar (QSO) and a dusty star-forming galaxy
(DSFG), both detected in [CII] and continuum emission as well as multiple
neighboring clumps detected only in [CII]. Three of these clumps form a (tidal)
tail that extends from the QSO in a straight direction to the west, covering a
projected distance of $\sim$ 10 kpc. This perturbed morphology, added to a
spatial distance of $\sim$ 20 kpc and a velocity offset of $\Delta{v}$ = 68 km
s$^{-1}$ between the QSO and the DSFG, strongly supports a merging scenario. By
fitting a spectral energy distribution model to the continuum data, we estimate
star formation rates of $\approx$ 402 $M_{\odot}$ yr$^{-1}$ for the QSO host
and $\approx$ 244 $M_{\odot}$ yr$^{-1}$ for the DSFG, which locate them on or
close to the main sequence of star-forming galaxies. The J2057-0030 QSO was
selected for being one of the brightest unobscured quasars at its redshift
while presenting a rather modest star formation rate. Based on a commonly
accepted paradigm regarding the formation of quasars, this result is expected
for a quasar that has already passed an obscured phase of rapid star formation
during a major merger. However, we see that the merger event in this system is
far from being finished, and it is rather likely somewhere between the first
pericenter and subsequent close passages. This is presumably another case of a
high-$z$ quasar residing in a high-density environment with a companion
obscured galaxy.
