(I'm playing it safe and inserting some up-front...
(... for those who haven't yet read the conclusion of the first "Double Duck" story arc and don't want to be unpleasantly surprised by my comments.)
Ah, me... I was always just a little afraid that the mysterious "Red Primerose" would turn out to be our charming Kay K. But I wanted so much to believe that Kay was nothing more than (1) Donald's Agency partner and (2) a potential rival for Daisy that I shoved the notion to the back of my mind until I had incontrovertible proof of her guilt. Said proof was not long in coming in this issue (and, IMHO, I think that Donald was deserving of a much more shocked reaction than merely sticking out his tongue in a pathetic manner akin to Wile E. Coyote just before the falling boulder strikes him). I am, however, legitimately disappointed that all Kay was after was The Agency's money and that the list-of-agents "McGuffin" was merely a ruse. If this "master spy" was willing to go to the trouble of pitting Agency agents and Marlo Burke against one another and impersonating the imprisoned Jay J with the aid of a mechanical robo-suit (does The Brain know about this egregious copyright infringement?), surely she could have had a slightly more sinister plan in mind than simply filching funds? ("Ah, but it's all part of her MASTER plan," replied David Xanatos, with a knowing chuckle.) There does appear to be one ray of hope for poor Kay K. Judging from the full list of existing Double Duck stories and the appearance of the December '09 TOPOLINO cover shown below, we can probably expect to see Kay (1) do battle with Donald and The Agency in future stories and (2) return to the side of the angels, up to and including teaming up with Double Duck once again. I hope this comes to pass; she's a good character and gave Daisy a serious romantic challenge that Donald's frequently exasperating inamorata desperately needs, to keep her humble if nothing else.
While the revelation that Kay was standing in for Jay J was not contradicted by any earlier gaffes of the "fourth Nephew Phooey" variety -- and yes, I did go back and check -- we did get a "left hand unaware of right hand" moment of sorts in that the opening scene of the arc, in issue #347, did not quite match up with what Kay revealed in this final chapter. If B-Berry had learned of Kay's treachery early on, then why, after stealing the laptop, did he warn Jay J that "lots of people are going to get hurt... starting with you!" and that he intended to "bring down the entire Agency!"? The story began and ended with different translators, and I suspect that wires got crossed somewhere during the transition. A pity; this was a surprisingly good read, given my low expectations at the outset.
The arc ends with The Agency's "Big Boss" being revealed to a stunned Donald. Place your bets, folks... mine's on Scrooge. Hey, the precedent was set (in Italy, at least) a number of years ago... and I just read the story in which the idea originated, no less. Watch this space for my review when I tackle the recently released DONALD DUCK CLASSICS: QUACK UP.