He has but one friend, ex-boxer Scrap (Morgan Freeman), noted for his barbed wit.
Out of the blue, waitress Maggie Fitzgerald (Hilary Swank) asks Frankie to become her trainer, in the hope that boxing will help her escape her dead-end job.
At first he refuses - a girl has no place in the boxing ring and, at 31, Maggie is too old - but her determination gradually wears him down.
Over a series of hard-fought encounters, Maggie discovers the person she always knew she could be, and Frankie realises the strength of his connection with this incredible and spirited young woman.
Eastwood is a towering physical presence, Freeman is a wonderfully charismatic foil, and Swank pushes herself to the limit in every sense, taking all of the punches for the sake of authenticity.
The movie delivers its own knock-out blow in the final minutes.
And when it lands, with staggering emotional force and precision - viewers will be out for the count.