This weeks episode of Enterpise started out normal enough when Dr. Flox was kidnapped. Turns out some other race nabbed him for the Klingons, who want him to work on some virus that's threatening the entire Klingon race.
Pretty tame so far, right?
It was, until a Bird of Prey attacked the Enterprise. A Klingon boarding party beamed aboard...and immediately stood out because they had normal foreheads!
Turns out this is the final link between the Klingons we've come to know and the old school guys from the original Desilu TV series. This is what Worf once described as something "We don't talk about".
The gist: the Klingons captures some augmented human DNA (human augments came up in a previous episode). They tried to make Klingon augments and were successful, until a normally nonfatal virus infected one of the augments and mutated.
So now the augmented and normal Klingons are in a race against time, to try and control or cure the virus until it wipes out the entire race. Episode to be continued next week...