A North Korean mogul digs up Japanese biological warfare from WWII. His plan is to use it against the US and, in the resulting chaos, reunify the two Koreas on the North's terms. But, of course, things don't work out how he wants because NUMA is in the right place at the right time.

Focus is on the kids though, which is less interesting. Dirk Pitt, Sr. only gets a supporting role, so it is just not the same.