When mountain runner Moire O'Sullivan's husband, Pete, took his own life, she was left with a stark choice: to weep forever over the glass of milk that had just spilt or to get on with the quarter that was still remaining.

'A quarter glass of milk' details the twelve months after Pete's passing. It charts the profound lows of being a recently widowed single mother who has lost her best friend and confidant. It also reveals how she resolves to stay strong for the sake of her children, ensuring they feel loved despite losing their father.

It tells how Moire makes the difficult decision to temporarily hang up her running shoes to replace them with hiking boots. By taking time out to become a Mountain Leader, by slowing down to a walking pace, she soon develops a different appreciation for the mountains and its people. And thanks to spending quality time within the hills, she soon realises her inner strength comes from embracing her fragility, something the mountains always show to those who dare approach them.

The book culminates in Moire returning to mountain running to take on the formidable Denis Rankin Round in the depths of winter, a ninety-kilometre circuit of the Mourne Mountains to be completed within twenty-four hours. Local mountain runners join her on this immense journey over thirty-nine of this range's peaks, helping her remember the dark struggles her husband went through while also showing how the mountains and its community can be such a healing strength.