Captain Anson, the officer commanding a British RASC Motor Ambulance Company in Tobruk, is suffering from battle fatigue and alcoholism. With the city about to be besieged by the German Afrika Korps, Anson and most of his unit are ordered to evacuate to Alexandria. During the evacuation, Anson, MSM Tom Pugh and two nurses, Sister Diana Murdoch and Sister Denise Norton, become separated from the others in an &lt;a href="Austin%20K2/Y"&gt;Austin K2/Y&lt;/a&gt; ambulance nicknamed "Katy". The quartet decide to drive across the desert back to British lines.