There are many changes between the play "Cosi" and Louis Nowra's adapted screenplay of Cosi. Firstly, in the play Doug burns down a toilet block and isn't blammed for it. Instead Julie takes the wrath for the incident saying that she threw a lighted cigarette down the toilet and that she was sorry and realised her mistake, therefore noone really discovered that it was Doug and the 'play project' continues uninhibited. Whereas, in the screenplay Doug openly burns down the entire Institutions theatre and is thrown into a closed ward or solitary confinement as punishment. As a result of this Dougs role in the play is revoked and given to Lewis (the director), and therefore gives Doug suitable reason to kill Lewis and jeopardise the play. Also, the manager of the institution who hired Lewis sees this tragedy as a lack of control and competence on Lewis' part, and no longer wishes to require his services as a director. .
In the play Lewis doesn't get fired because the incident of the toilet block burning down isn't a powerful enough to incident for him to lose his job, according to the minister of the institution. In the screenplay he is fired and despite this, continues to direct and act in "Cosi Fan Tutte" during the night time in secrecy. I think that this is a good change because it shows that Lewis isn't focused on the money of completely a job, and it shows that he cares for the opera and the world which Cosi fan Tutte tries to capture because otherwise he wouldn't bother continuing rehearsals in the secrecy of night, unpaid. .
In the original play Nick (Lewis' friend) openly admits to having an affair with Lewis' girlfriend Lucy, which relates to the issues of fidelity explored in the opera. In the screenplay Lewis assumes that Lucy is cheating on him with someone because she grows distant and vague during the time while he is directing the opera. These reasons are mainly due to the fact that she can't understand why he would care so much for directing an opera with a cast of mental patients.