  The inert Higgs-doublet model provides a simple framework to accommodate a
viable Higgs portal scalar dark matter candidate, together with other heavier
scalars of mass 100 GeV or more. We study the effect of next-to-leading order
(NLO) QCD corrections in this scenario in the context of the Large Hadron
Collider. ${\cal{O}}(\alpha_s)$ corrections to the gluon-gluon-Higgs effective
coupling have been taken into account in this study wherever appropriate. We
find such corrections have a significant impact on various kinematic
distributions and reduce scale uncertainties substantially. Fixed order NLO
results are matched to the {\sc Pythia8} parton shower (PS) and the di-fatjet
signal associated with the missing transverse momentum is analyzed, as this
channel has the ability to explore its entire parameter space during the next
phase of the LHC run. A closer look at the NLO+PS computation indicates a
sizable NLO effect together with a subdued contribution from associated
production of the heavy scalar compared to the pair production, thereby leading
to a refined analysis strategy during the multivariate analysis of this signal.
