While the first two seasons focus on the two's growing affection and Catherin's double life and secret love, the final season goes in a new direction when the first episode (a two-parter) has her finding out she is pregnant and being kidnapped. Her kidnapper makes it clear that all he wants is this child that is the offspring between Catherine and Vincent. We don't know much about this man, but we do know he is willing to wait the nine months or so it will take for the baby to be ready. And while Vincent, Catherine's co-workers and Catherine's ex-fiancé, Elliot Burch, all search for her, independently, of course, even when everyone else believes she is dead, Catherine eventually gives birth. Vincent feeling the child-bearing pain she is in, can finally sense her and comes to her rescue, unfortunately he is too late.
He arrives just in time for her captor (and the baby) to fly away in a helicopter and have Catherine tell him they have a child as she dies. This is basically where Catherine bows out of the series. Of course, she will be referenced many times since the focus of the season is to get revenge on this mysterious evil man and get back the son, but besides some flashbacks or memories, Linda Hamilton doesn't really make any appearances in the rest of the show.
The other 10 episodes of this season focus on Vincent slowly gaining information on the man who stole his child, and forming alliances with the other people who knew and loved Catherine. A new character, Diana, appears on the show early in the season and her job is to investigate Catherine's death. She eventually becomes aware of Vincent, first as someone who Catherine loved (since his name is in all of the books in her apartment), then in person, when she finds Vincent at Catherine's grave and sick. She nurses him back to health and Vincent takes her into his confidence.
Towards the end of the season Vincent eventually locates Gabriel (the person who has his son). Our hero is captured and kept locked up and tortured with images of Catherine, Vincent's search and finally their son, who has yet to be named. Eventually, Vincent breaks out and takes his son back to the underground world he should be in. Vincent names the boy Jacob after his father and, while there are still a few episodes left in the season, they feel much less important. With the imminent threat of finding Jacob gone, the series' final shows really don't seem to follow through. Sure there are some tied loose ends, but I have to say this show seems to have one of the weakest series finales I have ever seen.
Ultimately, this is a show for people who remember the series in its heyday. While it's good to see actors like Ron Perlman and Linda Hamilton, this series won't bring in any new fans with this release by any stretch of the imagination.