Complex sentence: When Vijay finds it, Roma decides to accompany him, not realizing he is not the real Don, and attempts to kill him, but DeSilva tells her about his plan, and she agrees to help him.
Split into simpler sentences: When Vijay finds it, Roma decides to accompany him, not realizing he is not the real Don. Roma attempts to kill Vijay (whom she believes is Don), but DeSilva tells her about his plan, and she agrees to help him.