Complex sentence: Determined to protect her sister, Marian crawls out onto a roof overlooking Percy and Fosco whilst they plot; but it begins to rain, and Marian, completely soaked, falls into a fever which shortly turns into typhus.
Split into simpler sentences: Determined to protect her sister, Marian crawls out onto a roof overlooking Sir Percival and Fosco whilst they plot. She falls into a fever which shortly turns into typhus.