  An $H^+ W^- Z$ vertex, i.e, the interaction connecting a singly charged
physical scalar to the $W^\pm,~Z$ gauge bosons is absent at the tree level in a
scalar sector comprising only $SU(2)_L$ doublets. However, the interaction can
be generated radiatively in such a case, an example of which is a two-Higgs
doublet model. In this study, we extend a two-Higgs doublet scenario by
additional $SU(2)_L$ scalar doublets. Upon endowing with appropriate discrete
symmetries, these additional doublets so introduced can furnish successful
candidates of dark matter. Interestingly, the same "dark" scalars can also
radiatively enhance the strength of the $H^+ W^- Z$ interaction. We compute the
$H^+ W^- Z$ vertex at one-loop in a non-linear gauge that eliminates certain
unphysical interactions. While all possible constraints are taken into account
in doing so, particular emphasis is given to the ones stemming from dark
matter. Correlations between the dark matter observables and the $H^+ W^- Z$
interaction-strength are studied. The study thus connects a radiatively
generated $H^+ W^- Z$ vertex to dark matter phenomenology.
