It's 1942 and in the Libyan war zone an ambulance with two frightened nurses, a sergeant major and a fatigued John Mills are desperate to reach the safety of Alexandria. This exciting premise is given a further twist of tension as they pick up a stray South African officer (Anthony Quayle) who is not all he seems to be.
The only reason he's on board is because he comes with three bottles of gin and poor old John Mills is gagging for a drink. In fact so much is his love for the grog that all that sustains him is the thought of sinking an ice cold beer once he gets to Alexandria.
Unfortunately his penchant for booze impacts badly on his driving skills and the group are thrown into danger. The added folly of taking on board their mysterious passenger adds an element of menace as they begin to suspect that he's a German spy. This idea of 'the enemy within' is exploited further as our plucky crew runs into a group of German soldiers. Seemingly surrounded on all sides they look doomed.
The cleverness of the film lies not only in the plot-line but also in the characterisation. Mills is becoming steadily more irrational as he desperately dreams of a beer "so ruddy cold there's a sort of dew on the outside of the glass". Meanwhile his well-meaning Sergeant is too careful to make decisive decisions and nurse Sylvia Sims is like a scared rabbit. With the crafty Quayle in their midst and the enemy closing in around them it seems impossible to imagine how escape can be possible. And with all this set in the relentless baking heat of the desert you'll be left gasping for a beer too.