At the sonorous boom of the foghorn, young Hester Stainsby gives an involuntary shudder. In the cavernous basement laundry room of the Poplar Hospital where she toils from dawn to dusk, there is fog too, damp, hot and swirling. Her fears are realised: her father, Fred has been badly injured in an accident in the East India Docks. Hester, already caring for her twin siblings, Harry and Polly, and the self-centred Granny Garter, now has the role of breadwinner. She determines, with the help of a staunch family friend, Big Peg, to embark on training as a nurse. The irrepressible Polly, her brother and disabled father, join in and together with their pet dog Puglet, they become The Poplar Penny Whistlers.