Cashback opens with the breakup of Ben and Suzy; Ben, played by Harry Potter's Sean Biggerstaff is a budding artist yet to find his way in life who suffers from insomnia after Suzy ends their relationship. Awake throughout the night Ben finds a job working nights in a supermarket in order to fill his waking hours during the night; the boredom of his job sees Ben begin to freeze time in his imagination and assess the shoppers and fellow workers.
His ability to freeze time slowly becomes real and Ben spends his evenings drawing frozen shoppers and fellow workers in various states of undress. During one of his frozen in time moments Ben sees another figure moving around despite time being stopped. Ben begins a relationship with fellow worker Sharon, played by Emilia Fox that ends when former girlfriend Suzy kisses Ben at a party. Remaining in his frozen in time world for a number of days Ben tries to find a way out of the mess of his love life before finally giving up. After breaking up with Sharon Ben sees his artwork displayed in a local gallery prompting a reconciliation with Sharon; following the rekindling of their romance Ben shares his secret of freezing time with Sharon.