Verbatim Tonic

Colourless liquid in a slim glass tube, holding a hard flat line at the top and not sloshing when it is shaken.

For 24 hours the drinker keeps everything exactly: every page read, route walked, word spoken, seal seen, and face passed can afterwards be recited, drawn, or written out to the letter, for the rest of the drinker's life. Nothing taken in during those 24 hours can be removed by any charm, curse, drug, blow, or spell that touches memory, and the drinker will know at once if something tries.