  The symmetries of string theory on ${\rm AdS}_3 \times {\rm S}^3 \times
\mathbb{T}^4$ at the dual of the symmetric product orbifold point are described
by a so-called Higher Spin Square (HSS). We show that the massive string
spectrum in this background organises itself in terms of representations of
this HSS, just as the matter in a conventional higher spin theory does so in
terms of representations of the higher spin algebra. In particular, the entire
untwisted sector of the orbifold can be viewed as the Fock space built out of
the multiparticle states of a single representation of the HSS, the so-called
`minimal' representation. The states in the twisted sector can be described in
terms of tensor products of a novel family of representations that are somewhat
larger than the minimal one.
