In spite of all the evidence, Mum pressed on as if things were normal. She got an electric wheelchair and a special microphone so she could continue teaching. When she couldn’t walk to the toilet without exhausting herself, she decided to lead a party of 30 to Tiritiri Matangi, the bird sanctuary island where she’d worked as a volunteer guide. This was stubborn, brave, almost heroic, but it was also delusional. Her disease was relentless — every day she was weaker than the day before — yet no-one seemed to know what to do. I decided to write her a letter.