Kat has a plan, and with one bright, unstoppable teenager, one bipolar dad off his meds, a dysfunctional family and a giant firework full of lithium, what could possibly go wrong?

When teenager KAT learns that her Uncle GILLIES is her biological dad, she runs away to Scotland to meet him, sabotaging her mum SARAH’s plan to move abroad. But she receives a startlingly frosty reception from his peculiar Scottish family – spearheaded by tyrannical grandmother CONSTANCE, who rules that Gillies is out of bounds. Kat escapes the guard of her nerdy cousin JAMES and runs off to meet Gillies in secret. But telling him she’s his daughter is harder than she anticipated – he thinks kids are stupid and boring – so she decides first to convince him otherwise. Since he’s an inventor, she comes up with a project of them building a home-made firework together,as a farewell tribute to his brother – planning to reveal her big secret at the launch. But Gillies is bipolar, a condition controlled by lithium carbonate, which, extraordinarily, is a crucial ingredient in fireworks. Kat recklessly encourages him to donate his meds to their cause, and is soon struggling with an increasingly manic Gillies – who becomes fixated on her mum (his long lost love), and turns the firework into a giant bomb, forcing Kat to face the consequences of her naivety and deceit.