Definitely not up to Nova's usual high standards. The documentary tries to create a greater sense of mystery than is warranted.
The sword, the authors conclude, must have been made with crucible steel, which was not available until the 19th century ... in Europe. Yet, a) they say it was available in the Middle East, which the Vikings had trade ties with, and b) they show a guy making crucible steel using nothing more than bricks, mortar and clay for an oven and crucible vessel, all of which were available anywhere.
Surely, the Vikings could have picked up this bit of technology in their travels. But, no, the authors make a muddled array of suggestions: maybe the sword maker was in France or with the Church, or using steel ingots imported from the Middle East. What is the answer? There is none given.
Why did only the Vikings have these swords? This could have been a nice little historical story. But the mystery element was way over-played, and the science element was insufficient to warrant a Nova program.
Why is it that so many programs (especially National Geographic) feel they have to hyper-hype? Perhaps documentary makers are spreading their material too thin; there's only so many subjects, and so many times people will watch the same story retold. This one reminds me of the one on the Titanic rivets, with some of the same electron microscopy and tensile strength tests.
They should have done less on the pseudo-mystery angle and done more that the viewer might not know about the science and history of steel. Heck, it could have been part of a series on the subject; another episode could talk about Krupp steel and its importance in history.
But all we see with this Viking sword is that it is made of simple crucible steel made of iron ore, a bit of carbon, and some glass, etc., to remove impurities. I kept waiting for them to tell me something surprising, like they added tungsten or chromium, but no such luck.
The most surprising aspect was how easy it is to produce steel, and that I could do it in my backyard if I had some iron ore, like the guy in the film. Good to know, in case I need to make a strong sword some day. Except there's a catch: you can't just dig up any old iron ore. You need an ore that's free of impurities, which is why Swedish steel is still renown.
So where did they get the ore used for the demonstration? They don't say; frankly, it looked like recycled iron, or at least carefully selected ore free of undesirable impurities like sulfur. This may be the reason for the rather muted praise from the test lab, which the documentary makers claim was high praise. It looks to me like the modern demonstration project was rigged.
Secrets? What secrets? That it was made with a rudimentary crucible method available during that period of history? As to answers to the "mysteries" posed by the producers, there aren't any given. Bad science, muddled mysteries, not Nova.