Complex sentence: During the investigation, in which Nick breaches protocol several times and makes contact with an American nightclub owner, Joyce, he discovers that Sato is fighting a gang war with a notorious crime boss, Sugai.
Split into simpler sentences: During the investigation Nick breaches protocol several times and also makes contact with an American nightclub hostess, Joyce. Through her, he discovers that Sato is fighting a gang war with a notorious crime boss, Sugai.