Originally written in Italian, there's about 40 others, many seem to be spoofs on adult novels. They've achieved sort of a cult following among my 4th grade students (well, 4 of them trade them back and forth, I guess that's how a literary cult works)
Geronimo Stilto, Thea stilton, Trap Stilton, Benjamin Stilton. Are mice who solve a mystery.It all started when Thea discovered an old, mysterious map. It showed a secret treasure hidden on a faraway island. In no time at all, Thea dragged her brother and cousin into her treasure hunt. It was an adventure i'd never forget.