A debut novel, Inside the Whale,features two characters separated by fate. In the summer of 1939, Stevie and Michael are young lovers. They are torn apart by war when Michael is sent to fight in Africa and doesn't return. Half a century later, Stevie is recently widowed and struggling to tell her family the truth about her complicated past. Meanwhile, Michael is preparing for a move to hospital. Unable to speak, he writes down his story for a sympathetic healthcare worker. Their stories unfold in alternating chapters told in their distinct voices.

The Guardian states that "Rooney confidently moves between two narrators and shifting times, vividly recreating Blitz-torn London and the Africa of the same period", and calls it "a deeply affecting story of thwarted circumstances and belated wisdom". "Inside the Whale" was nominated for the Costa First Novel Award.