How can I be so sure, after all this time? Because musical memory does not fade like other faculties. I may have trouble remembering the names of my daughters-in-law, but I can recall every note of the first ‘Eroica’ Symphony I heard, aged eleven, conducted by the cranky and incontrovertible Otto Klemperer. I may be cheating a bit since I attended both rehearsals and performance. But the fact that I can vouch for every particle of this experience when I could not, if mugged at a cash-point, remember my PIN number to save my life, confirms the indelibility of musical memory.

There is empirical confirmation of this supposition. The neurologist Oliver Sacks, in a case-history entitled The Man Who Mistook his Wife for a Hat, observed an elderly musician who was suffering from an advanced form of Alzheimer’s disease and unable to tell his wife from his headgear. The only way he could get dressed was by humming a Schumann song whose melody, perfectly remembered, provided a framework in which he could fulfil such complex tasks as tying his shoes and finding his hat. The case-history, converted by Michael Nyman into an effective chamber opera, is a moving testimony to the residual power of music in age-worn minds. In my own case, unimpaired musical memory allows me to compare with a high degree of certainty the sounds I hear today with those I heard as a boy. When I judge that Peter Stemp is employing a device that was patented by a violinist who walked out of my life forty years ago, I do so with full confidence in my judgement – knowing, also, that I am the only man alive who can testify to the coincidence.

There are, as I have said, no recordings of the vanished violinist, nor any mentions in musical literature. He left the stage before the curtain rose, and he took with him half of my being and all of my hopes. I have missed him, unmentioned, every day of my subsequent half-life. I cannot yet bring myself to utter his name, but as Peter Stemp’s echo of his trademark trick pricks my ears and floods my eyes, I need no further proof to know that I have somehow picked up his scent and may be on the way to retrieving a part of the life that was stolen from me by that unforgettable time-bandit.

This is not suspicion or surmise; nothing resembling the did-we, didn’t-we waltz with Sandra Adams. This is a dead-cert sighting of a suspect who stole the inner, better half of me and left behind the bitter exterior. Hearing Peter Stemp of Oldbridge play a note that defies the passage of time, I know beyond a possibility of doubt that my devourer liveth – and that, come what may, I shall track him down before I die.