Complex sentence: Though at first well behaved and decorous, he soon shocked the society of Skvoreshniki by several ridiculous but aggressively antisocial action; he was partly excused owing to a medical diagnosis of an acute episode of'brain fever'.
Split into simpler sentences: Though at first well behaved and decorous, he suddenly shocks the society of Skvoreshniki with several ridiculous but aggressively antisocial actions. Society is outraged, but he is partly forgiven owing to a medical diagnosis of an acute episode of'brain fever'.