  The dynamics of isolated-photon plus two-jet production in $pp$ collisions at
a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the
LHC using a dataset corresponding to an integrated luminosity of 36.1
fb$^{-1}$. Cross sections are measured as functions of a variety of
observables, including angular correlations and invariant masses of the objects
in the final state, $\gamma+jet+jet$. Measurements are also performed in
phase-space regions enriched in each of the two underlying physical mechanisms,
namely direct and fragmentation processes. The measurements cover the range of
photon (jet) transverse momenta from 150 GeV (100 GeV) to 2 TeV. The tree-level
plus parton-shower predictions from SHERPA and PYTHIA as well as the
next-to-leading-order QCD predictions from SHERPA are compared with the
measurements. The next-to-leading-order QCD predictions describe the data
adequately in shape and normalisation except for regions of phase space such as
those with high values of the invariant mass or rapidity separation of the two
jets, where the predictions overestimate the data.
