In this article, it is argued that obsessive-compulsive disorder (OCD) with overt compulsions, where there is overvalued ideation, is primarily a disorder of the imagination and hence, by implication, psychological therapy should principally address the client’s imagination, rather than other cognitive processes. According to this model, the OCD client imagines a state of affairs which is then taken ‘as if it were a reality and does so because of the persuasive influence of an imaginary narrative fiction. This narrative is replayed, often in condensed form, in the OCD context and leads the client into a chain of maladaptive inferences about a possible state of affairs. The client then acts in accordance with what might be present rather than what is actually present. An inference-based approach (IBA) which directly addresses and challenges the imaginary narrative of the client is outlined, with clinical illustrations. The IBA approach complements other cognitive-behavioral therapy (CBT) and can be used in conjunction with existing CBT methods which focus more on modifying the interpretations and secondary appraisals subsequent to primary inferences.