Complex sentence: Finding none, he went to London then back to Paris, and finally returned to Scotland in November 1613 disguised as a soldier named John Watson, and began to preach in secret, celebrating mass clandestinely in private homes.
Split into simpler sentences: Finding none, he went to London, then back to Paris, and finally returned to Scotland in November 1613 disguised as a soldier named John Watson. Thereafter he began to preach in secret, celebrating mass clandestinely in private homes.