A story based on the life of Elizabeth Kenny (Rosalind Russell). It begins, shortly before the start of World War I, as she takes up work as a nurse in the bush' near her parents farm - not far from Toowoomba (a regional centre in rural Queensland, Australia). Kenny shows a great deal of skill in her new job and is much loved by all those in her care.

One night she is called out to a child named Doreen McIntyre (Doreen McCann), whose symptoms include contorted limbs and a stiffly curved spine. Not knowing what it could be she describes the symptoms, by telegraph, to a doctor friend - Dr Aeneas McDonnell (Alexander Know) - in Toowoomba. His reply indicates that the disease she has described is a clear-cut case of Infantile paralysis (Polio). His advice is to treat the child, according to the symptoms ... no more.

Nurse Kenny is unsure what to do but, nevertheless, does what she thinks is best - which is to wrap the childs stiffened limbs in hot woolen sheets to relieve what she calls 'spasms'. Eventually the treatment seems to work, in that it relieves the twisted limbs but afterwards she discovers that the child is unable to move her legs. Again, unsure of what to do, but naïve enough to try anything, she decides that the childs muscles must have forgotten how to move and so proceeds to 're-educate' them.

While treating Doreen, five other cases of the same disease arise in her area and she treats them all in the same way. All six children achieve a full recovery, however, Kenny is unaware of the importance of her accomplishment until she goes to see her friend Dr McDonnell in nearby Toowoomba.

The reason for her visit to Toowoomba is to inform McDonnell of her impending marriage to a long time friend, Kevin Connors (Dean Jagger), who is just back from the War. According to nursing regulations at the time, her marriage means that she will no longer able to continue work. However, while she is there, McDonnell shows her the impact which a recent outbreak of Polio has had on the children around Toowoomba and cites a figure of 80 percent who have ended up with permanent disabilities and who face lives spent in callipers and on crutches. When Kenny shows Doreen (whom she happened to bring along for the ride) to him, he cant believe how healthy she is and is even more surprised when Kenny informs him that her five other patients are equally as well.

He takes Kenny in to meet an Orthopedic specialist at the hospital, a Dr Brack (Philip Merivale), who hears Kennys story - and then examines Doreen - however he dismisses her ideas as foolish nonsense and says that it is obvious that Doreen must never have had Polio in the first place.

Brack explains that every textbook ever written on the subject states that the muscles which extend as the childs limbs twist, is the one affected by Polio and that it was the Polio which caused it to become weak in the first place. He adds that the muscle on the opposite side of the limb takes control of it and it ends up pulling the limb out of alignment.

However, Kennys treatment is based on just the opposite; that it is the shortened muscle which is diseased and that it has gone into what she calls a 'spasm', placing the sound muscle in a position where it is not being used - thus losing its ability to function. Her theory involves 're-educating' the under-used muscles by exercising until they are strong enough to resume normal use.

This begins a forty year feud between the two, with Kenny seeing, first hand, the evidence that her treatment works (even with children Brack has given up on) and Brack clinging steadfastly to his established ideas - which involve immobilising the patients limbs rather than mobilising them - a treatment which Kenny sees as making the condition worse.

Meanwhile, Kenny puts her marriage to Connors on hold, as she takes on the medical profession, and Connors is re-called for active service in Europe.

Every time Kenny tries to have her treatment acknowledged, the medical establishment thwarts her but despite this, she gains notoriety by establishing clinics to prove her point. Children come form everywhere to be treated by her - with great success. But, still, the establishment will not budge. Eventually, a sympathetic Medical Director (John Litel), who is motivated by the great deal of public support being shown for Sister Kenny, sets up a Royal Commission. However, the Commission is dominated by Brack and other Orthopaedic specialists who convince it to reject Kenny's ideas - as well as her right to practice - threatening to prosecute her if she does.

Time and time again she postpones her marriage to Connors in order to fight for her ideas and, time and time again, he continues to wait and gives his support until, eventually, it gets too much for him and he leaves, leaving both of he and Kenny heart broken.

Kenny, her fame having spread world-wide, is invited to work in England where, once again, she achieves excellent results but is dismissed by the medical establishment. There to it forces her to cease her work. She returns home for a while only to be invited to work in the United States. When she arrives she is hailed as an anti-establishment rebel and a hero to the all the victims of Polio, only to be thwarted, once again by the inability of the medical profession to think laterally.

Dejected and about to return home to Australia, Kenny receives an last minute invitation to practice in Minnesota, where a recent outbreak of Polio has motivated the State's Health authorities to try out her ideas. With the support of the State's medical system, she achieves outstanding success but, once again, a Federal Inquiry finds her ideas to have no substance.

Despite this, Kenny seems to take finds contentment in spreading the word among sympathetic doctors and seeing the benefits she can bring to her hoards of thankful patients.

As the movie closes, Kenny is celebrating her birthday with her patients singing 'Happy Birthday' to her. Having given up the chance for love and having devoted her entire life to fight the medical status quo, she realises that her life has not been wasted - not in the least.