Cassandra McDermott was 19 years old, loved by a houseful of sisters, and had just found the strength to leave a violent boyfriend. On 26 November 2001, while her mother was on a holiday Cassandra herself had insisted she take, she was beaten and left to die on a bedroom floor in Norbury, south London.

In 2002, her ex-boyfriend Mario Celaire stood trial at the Old Bailey. The jury deliberated for less than 3 hours and acquitted him. Under the rule against double jeopardy, a principle around 800 years old, that verdict could never be revisited.

5 years later, in Walthamstow, a 19-year-old woman called Kara Hoyte was attacked with a hammer and left for dead. She survived. She could not speak. Her mother sat beside the hospital bed and began writing names on a whiteboard.

This is the story of what Kara Hoyte knew, what she did with it, and how the Criminal Justice Act 2003 turned a permanent acquittal into a retrial. It is also the story of a family who built something in Cassandra's name.

Content note: this episode discusses domestic abuse and fatal violence against women. Details are kept to what the story requires.

Support: in the UK, the 24-hour National Domestic Abuse Helpline is 0808 2000 247. In Ireland, Women's Aid is 1800 341 900. The Cassandra Centre can be found at cassandracentre.org.uk.