In London in the mid-1920s, a young Australian and her aunt are each on a journey of self-discovery - one by attempting to swim the English Channel, the other to rediscover the woman she used to be.

It's 1925, and 15-year-old Catherine Quick longs to feel once more the warm waters of her home, to strike out into the ocean off the Torres Strait Islands and swim, as she's done since she was a tiny child. But with her recent move to London, where she lives with her aunt Louisa, Catherine feels that everything she values has been stripped away.

Louisa, a busy, confident London surgeon who fought boldly for equality for women, holds definite views on the behaviour of her young niece. She wants Catherine to pursue an education, just as she did, to ensure her future freedom. Since Catherine arrived, however, Louisa's every step seems to be wrong, and she is finding it harder and harder to block painful memories from her past.

It takes the influence of enigmatic American banker Manfred Lear Black to convince Louisa to come to New York, where Catherine can test her mettle against the first women in the world to swim the English Channel. And where, unexpectedly, Louisa can finally listen to what her own heart tells her.