This in-depth study demonstrates the value of single-case research, as well as confirming the value of the particular method that was studied. Method of Levels (MOL) Therapy is described and applied to the case of a woman whose husband died. MOL Therapy is derived from Perceptual Control Theory. Session to session changes within the woman were quantified by means of Q Methodology and Personal Construct analyses. MOL Therapy identifies the important conditions for therapy change to occur. The case study results were supportive of the ideas of MOL Therapy.