  We propose a natural $ S_4 \times SO(10) $ supersymmetric grand unified
theory of flavour with an auxiliary $\mathbb{Z}_4^2 \times \mathbb{Z}_4^R$
symmetry, based on small Higgs representations (nothing larger than an adjoint)
and hence a type-I seesaw mechanism. The Yukawa structure of all fermions is
determined by the hierarchical vacuum expectation values of three $ S_4 $
triplet flavons, with CSD3 vacuum alignments, where up-type quarks and
neutrinos couple to one Higgs $\mathbf{10}$, and the down-type quarks and
charged leptons couple to a second Higgs $\mathbf{10}$. The Yukawa matrices are
obtained from sums of low-rank matrices, where each matrix in the sum naturally
accounts for the mass of a particular family, as in sequential dominance in the
neutrino sector, which predicts a normal neutrino mass hierarchy. The model
accurately fits all available quark and lepton data, with predictions for the
leptonic $CP$ phase in 95$\%$ credible intervals given by $ 281^\circ <
\delta^\ell < 308^\circ $ and $ 225^\circ < \delta^\ell < 253^\circ $. The
model reduces to the MSSM, with the two Higgs doublets emerging from the two
Higgs $\mathbf{10}$s without mixing, and we demonstrate how a $\mu$ term of
$\mathcal{O}$(TeV) can be realised, as well as doublet-triplet splitting, with
Planck scale operators controlled by symmetry, leading to acceptable proton
decay.
