  We present the analysis of archival Very Large Telescope (VLT) Multi-Unit
Spectroscopic Explorer (MUSE) observations of 179 HII regions in the
star-forming double-ring collisional galaxy AM 0644-741 at 98.6 Mpc. We
determined ionic abundances of He, N, O and Fe using the direct method for the
brightest H II region (ID 39); we report $\log\rm{(\frac{N}{O})}=-1.3\pm0.2$
and $12+\log\rm{(\frac{O}{H})}=8.9\pm0.2$. We also find the so-called
`blue-bump', broad He II $\lambda4686$, in the spectrum of this knot of massive
star-formation; its luminosity being consistent with the presence of $\sim430$
Wolf-Rayet (WR) stars of the Nitrogen late-type. We determined the O abundances
for 137 HII regions using the strong-line method; we report a median value of
$12+\log\rm{(\frac{O}{H})}=8.5\pm0.8$. The location of three objects, including
the WR complex, coincide with that of an Ultra Luminous X-ray source. Nebular
He II is not detected in any H II region. We investigate the physical
mechanisms responsible for the observed spectral lines using appropriate
diagnostic diagrams and ionization models. We find that the H II regions are
being photoionized by star clusters with ages $\sim2.5-20$ Myr and ionization
potential $-3.5<$$\log\langle U\rangle$$<-3.0$. In these diagrams, a binary
population is needed to reproduce the observables considered in this work.
