A ten-year-old boy manages to first lose his sister in 11th-century Britain (via his
father’s time machine) and then lose his Pop somewhere in the 9th-century Bulgarian Empire.
The sister is found fairly quickly, but not until thirty years later does an archeology
colleague bring a clue as to exactly where his father might be.
When he’d left the room for a moment Sis dared me to send her somewhere.