Three small-time crooks, Griff Derren Nesbitt, Len Keith Faulkner, and Len's brother Alec William Morgan Sheppard, pull off a bank robbery just after closing time on a Saturday before the Easter Monday bank holiday. The plan is simple: grab the cash and vanish, but the heist takes a sharp turn when two cleaners unexpectedly arrive, turning what should be a clean exit into a tense standoff inside a bank that can’t be emptied quickly enough.
Stuck inside the bank’s airtight strongroom are the manager, Mr. Spencer Colin Gordon, and his secretary Rose Taylor Ann Lynn. The crooks momentarily celebrate their escape, yet they soon realize the two hostages will suffocate if the building remains sealed and unventilated for days. Their predicament tightens the suspense: the robbers must act quickly before the Easter weekend crowds—or the clock runs out.
With no easy way out, Griff and Len improvise a plan to save themselves and possibly the hostages. They decide to leave the strongroom keys in a telephone box and alert the police with an anonymous call. Alec volunteers to handle the crucial task, but tragedy strikes when he is killed in a road accident while making his escape. The loss hits Len hard, and the news of his brother’s death drives a dangerous anger through him: he blames the two bank employees and swears he won’t help Griff free them.
Meanwhile, the two inside the vault recalculate their dwindling air supply—the couple can manage at most twelve hours if they conserve every breath, a race against time that grows more desperate by the minute. They cling to the hope of rescue, even as the manager’s friends, who were supposed to meet him at the bank, drift away to their weekend rounds of golf, unaware of the peril behind the vault door. Rose’s family believes she is away for the weekend, leaving her fate uncertain to those waiting outside.
Len makes another attempt to recover his brother’s belongings from the coroner’s office, hoping to reclaim the strongroom keys that could unlock their fate. He is told that the items cannot be released without police permission, adding another layer of delay and tension to an already fragile plan. The police quickly connect the dots: the key’s origin ties back to the bank, and the mystery of how someone could possess both keys grows thornier by the minute. The investigators track down the key’s maker and begin to piece together which bank it belongs to, while the initial suspicion falls on Mr. Spencer. It becomes clear, however, that no single bank employee should hold both keys, signaling a far more dangerous breach of the system.
The pursuit intensifies as Len and Griff drill a hole through the strongroom door in a bid to reach the occupants. The Inspector, initially cautious, allows the operation to continue as the tension escalates. At last the vault door opens, and the bank manager is pulled free, barely alive. The moment is shattered by a grim discovery—the police report a casualty inside the strongroom. The line rings through the scene, a jarring reminder of the grave consequences that followed the attempted rescue:
> This one (Rose) is DEAD sir!
The grim revelation settles over Griff and Len, who stand face to face with the reality that murder was a capital offense at the time. Their plan to survive through a botched bank heist has unravelled into a dangerous, fatal trap, leaving the outcome unresolved for the two convicts while the hostages’ fate hangs in the balance and the law closes in.
