A light little mystery in the vein of The Mad Scientists Club or the Bill Bergson series. Undersized genius Mini-Minor Morris and his pals in the Queen Street Gang tackle crooks and spies with juvenile ingenuity.
When Mini-Minor's scientist father disappears, along with his newly-invented energy source, the Silver Egg, he is suspected of defecting to a foreign power. Mini-Minor knows this can't be true, and with his pals, he sets out to find and rescue his father. They meet every challenge with aplomb, sometimes with Mini-Minor's scientific know-how, sometimes with a kid's knowledge of how grown-ups think (or don't).
It doesn't have the underlying seriousness of Emil and the Detectives or of The Horse Without a Head (aka A Hundred Million Francs), and the suspense never becomes too unnerving, but it remains an enjoyable read.