The potential energy profile for the atomic iodine plus water dimer reaction I + (H2O)(2) -> HI + (H2O)OH has been explored using the "Gold Standard" CCSD(T) method with quadruple-zeta correlation-consistent basis sets. The corresponding information for the reverse reaction HI + (H2O)OH -> I + (H2O)(2) is also derived. Both zero-point vibrational energies (ZPVEs) and spin-orbit (SO) coupling are considered, and these notably alter the classical energetic-s. On the basis of the CCSD(T)/cc-pVQZ-PP results, including ZPVE and SO coupling, the forward reaction is found to be endothermic by 47.4 kcal/mol, implying a significant exothermicity for the reverse reaction. The entrance complex I center dot center dot center dot(H2O)(2) is bound by 1.8 kcal/mol, and this dissociation energy is significantly affected by SO coupling. The reaction barrier lies 45.1 kcal/mol higher than the reactants. The exit complex HI center dot center dot center dot(H2O)OH is bound by 3.0 kcal/mol relative to the asymptotic limit. At every level of theory, the reverse reaction HI + (H2O)OH I + (H2O)(2) proceeds without a barrier. Compared with the analogous water monomer reaction I + H2O -> HI + OH, the additional water molecule reduces the relative energies of the entrance stationary point, transition state, and exit complex by 3-5 kcal/mol. The I + (H2O)(2) reaction is related to the valence isoelectronic bromine and chlorine reactions but is distinctly different from the F + (H2O)(2) system.