The primary goal of the present work was to model pathways of the light-induced hydration reaction in Dreiklang by using complementary simulation tools as compared to Ref. . We explored the relief of the excited-state PES from the CT level with the state-averaged complete active space SCF method and located conical intersection points with the ground state potential surface. Analysis of further evolution of the system in the ground state by the QM/MM method allowed us to find the route to the OFF-state structure via the firmly established reaction intermediate X, thus providing full characterization of the mechanism of the hydration reaction in Dreiklang. We also consider alternative protonation states of the amino acid residues next to the chromophore and discuss the role of proton wires in Dreiklang.