  We present a new high-precision strong lensing model of PLCK G287.0$+$32.9, a
massive lens galaxy cluster at $z=0.383$, with the aim to get an accurate
estimation of its effective Einstein radius and total mass distribution. We
also present a spectroscopic catalog containing accurate redshift measurements
for 490 objects, including multiply-lensed sources and cluster member galaxies.
We exploit high-quality spectroscopic data from three pointings of the VLT
Multi Unit Spectroscopic Explorer, covering a central $3~\rm{arcmin}^2$ region
of the cluster. We complete the spectroscopic catalog by including redshift
measurements from VLT-VIMOS and KECK-DEIMOS. We identify 129 spectroscopic
cluster member galaxies, with redshift values $0.360 \leq z \leq 0.405$ and
$m_{\rm{F160W}} \leq 21$, and 24 photometric ones identified with a
Convolutional Neural Network from ancillary HST imaging. We also identify 114
multiple images from 28 background sources, of which 84 images from 16 sources
are new and the remaining ones were identified in previous work. The
best-fitting lens model shows a root mean square separation value between the
predicted and observed positions of the multiple images of $0.75''$,
corresponding to an improvement in reconstructing the observed positions of the
multiple images of a factor of $2.5$ with respect to previous models. Using the
predictive power of our new lens model we find 3 new multiple images and we
confirm the configuration of three systems of multiple images that were not
used for the optimization of the model. The derived total mass distribution
confirms this cluster to be a very prominent gravitational lens with an
effective Einstein $\theta_{E} = 43.4'' \pm 0.1''$, that is in agreement with
previous estimates and corresponds to a total mass enclosed in the critical
curve of $M_E = {3.33}_{-0.07}^{+0.02} \times{ 10^{14} M_\odot}$.
