Complex sentence: There would be agents waiting to immediately capture them once they emerged through the Hong Kong door, so they decide to fly to Macau to seek help from one of the Nexus' contacts before taking a boat into Hong Kong.
Split into simpler sentences: There would be agents waiting to immediately capture them once they emerged through the door. They decide to fly to Macau to seek help from one of the Nexus' contacts before taking a boat to Hong Kong.