This week’s Fringe was one of best of the season (so far). As the episode opens, an cinnamon-scented airborne toxin causes people to die by being “suffocated from the inside-out,” as Walter puts it. We also learn more about the Bishop family tree.

Right away, Olivia realizes that one of the victims at a wedding party was a Holocaust survivor. The villain of the episode, a Nazi sympathizer, had developed a lethal formula that could pinpoint specific victims based on their DNA. All it needed was a heat-source dispersed into the air to be effective.

Much of the information the bad guy was using for his research came from an experiment conducted by Walter’s father. Peter’s grandfather was Dr. Robert Bishoff, a U.S. spy who worked in Germany in the World War II era.

The highlight of the hour was the tension between Walter and Peter. Walter wanted to see his father’s research notes, but Peter told him he’d sold them 10 years ago (while Walter was committed to St. Claire’s). Peter’s says that he needed the cash but did admit there was more to it. Witnessing how far Walter and Peter have come as father and son, it is easy to forget that Peter resented Walter for his upbringing and Walter’s abandonment. Its clear selling those books, at that time, was a way of acting out against those feelings.

In the end, Walter saves the day by killing the villain in a very public place, no doubt out of guilt as much as anything else.

At the end of the episode, Walter tells Olivia, “Family is very important to me; there’s nothing I wouldn’t do.” A fact that will surely be proven more and more as the story of Peter and the alternate word continues to unfold.