Complex sentence: When his superiors freeze him out of the case, Gallagher begins his own investigations which propel him into a web of drugs and vice, corruption and cover-up-an intricate web that implicates some of the city's most senior figures.
Split into simpler sentences: When his superiors freeze him out of the case, Gallagher begins his own investigations. His investigation propels him into a web of drugs and vice, corruption and cover-up-an intricate web that implicates some of the city's most senior figures.