The play is in four parts. Each opens with the sound of a bell. After this the lights fade up to reveal an illuminated strip along which a woman, May, paces back and forth, nine steps within a one-metre stretch. In each part, the light will be somewhat darker than in the preceding one. Therefore, it is darkest when the strip is lit up without May at the very end. Correspondingly, the bell gets slightly softer each time. Beckett introduced a “Dim spot on face during halts at R [right] and L [left]” so that May’s face would be visible during her monologues.
The play has a very musical structure and timing is critical. “The walking should be like a metronome”, Beckett instructed, “one length must be measured in exactly nine seconds.”  “These ‘life-long stretches of walking,’ he told his German May, Hildegard Schmahl, are ‘the centre of the play; everything else is secondary’.” 
To ensure that every step could be heard “sandpaper was attached to the soles of [Billie] Whitelaw’s soft ballet slippers”  during the London premiere.
As she covers the nine paces (seven in earlier printed texts) she hugs herself, the arms crossed, with the hands clasping the shoulders in front. ‘When you walk, you slump together, when you speak, you straighten up a bit.’ Schmahl asked Beckett if May’s posture was supposed to express fear? “No, not fear. It expresses that May is there exclusively for herself. She is isolated.” 
One of a long line of Beckett protagonists whose name begins with an M, May is a woman in her forties (who should however appear “ageless”  according to Beckett). She paces back and forth on a strip of bare landing outside her dying – if not already dead – mother’s room (a vertical ray of light not in the printed text suggests a door barely ajar).
The woman, clearly a shadow of her former self, wears tattered nightwear and has a ghostly pallor. Beckett said: “One could go very far towards making the costume quite unrealistic, unreal. It could, however, also be an old dressing-gown, worked like a cobweb … It is the costume of a ghost.”  “You feel cold. The whole time, in the way you hold your body too. Everything is frost and night.”  The adjective ‘ghostly’ is used frequently – by Beckett himself and others – to describe various aspects of Footfalls.
The play – significantly – only has a semblance of a plot.
May’s mother is only ever heard. We learn that she is apparently ninety years old and in poor health. The more likely truth is that she is a creation of May’s mind, especially when one examines Beckett’s earlier drafts.