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The interconversion of nonactivated alkenes and alcohols, catalyzed by (de)hydratases, has great potential in biotechnology for the generation of fine and bulk chemicals. LinD is a cofactor-independent enzyme that catalyzes the reversible (de)hydration of the tertiary alcohol (S)-linalool to the triene β-myrcene and also its isomerization to the primary alcohol geraniol. Structure-informed mutagenesis of LinD, followed by activity studies, confirmed essential roles for residues C171, C180, and H129 in water activation for the hydration of β-myrcene to linalool. However, no evidence of covalent thioterpene intermediates was found using either X-ray crystallography, mass spectrometry, or QM/MM nudged elastic band simulations. Labeling and NMR experiments confirmed a role for residue D39 in (de)protonation of the linalool carbon C10 in the isomerization of linalool to geraniol and also the intermediacy of β-myrcene in this isomerization reaction. X-ray, molecular dynamics, and activity studies also suggested a significant role in catalysis for a mobile methionine residue M125, which exists in substantially altered orientations in different mutant structures A.C. was funded by grant BB/P005578/1 from the BBSRC. We thank Dr Johan P. Turkenburg and Mr Sam Hart for assistance with X-ray data collection and the Diamond Light Source for access to beamlines I02, I03 and I04-1 under proposal number mx-9948. The York Centre of Excellence in Mass Spectrometry was created thanks to a major capital investment through Science City York, supported by Yorkshire Forward with funds from the Northern Way Initiative, and subsequent support from EPSRC (EP/K039660/1; EP/M028127/1). This study was also supported in part by the European Research Council Horizon 2020 research and innovation program (ERC-2015- StG-679001, S.O.), Spanish MINECO (project PGC2018-102192-B-I00, S.O.), Generalitat de Catalunya for the emerging group CompBioLab (2017 SGR-1707); Juan de la Cierva-Incorporación fellowship IJCI2017-34129, J. I.F), and Marie Curie EnzVolNet fellowship (H2020-MSCA-IF-2016-753045, J. I. F)