Joan Lennon 
Leif Frond and Quickfingers [PDF ebook] 

A wandering pedlar turns up in Leif”s village, much to the delight of the Vikings of Frondfell. Only Leif suspects there”s something not quite right about the small, wrinkly old man.
As belongings start to go missing in the village and the pedlar is suddenly nowhere to be found, Leif”s suspicions are confirmed.
Can Leif track down the disappearing pedlar, survive insane flying inventions, and prove himself to be a hero once and for all?