The protagonist was a young man about to head off to University to study maths (physics) and he's been awarded an important scholarship. He hears about experiments with tachyons going on at the university and manages to get an internship working for the project. He spends some months involved, getting close to the scientists and other students. The project leader is really charismatic.
He keeps seeing random children running around, and then on the day the device gets brought up to full power he sees a group of these children run out of the machine and never come back. The implication is made that these were the children stolen from Hamelin and that the project leader was the Pied Piper and the time machine was the source of the legend.
I read it in the late 1980's or early 1990's.