In this, the first of two related papers, the process is examined by which a couple were helped to separate, temporarily and emotionally, through a brief offer of psychodynamic therapy. The therapy comprised six weekly sessions of one hour's duration, an input often considered inadequate for effective analytic psychotherapy. The paper examines the interrelationship between an unconscious shared phantasy which had produced deadlock in the marriage and two structural aspects of the therapeutic offer - its brevity and the decision to see the partners separately. The concept of shared phantasy is discussed in the second of these papers which describes in the context of one model for outcome assessment, in what terms the therapy might be said to have been effective.