Code Name 711 (HarperCollins, October 2013) is the second of the series about an ordinary skate-boarding guy named Linc who just happens to be a dead ringer for a spy kid, Ben, who works for a top secret government agency, Pandora. And the folks at Pandora hope this likeness will come in useful, as it did in Linc's first adventure, and so they whisk Linc off to DC to help foil a plot to assassinate the President.
It's not your ordinary assassination attempt. The would-be assailant is plotting to use one of the Dangerous Doubles that are a chief concern of Pandora's--a magical coat that once belonged to George Washington, that protects its wearer from any bodily harm. Linc and Ben are both charged with finding the Dangerous Double before the bad guy does, and a chase around Washington ensues, with the President's daughter, Amy, enthusiastically getting in on the action.
It's fast paced and fun, and though it does strain credulity early and often (not the coat--I can accept magical doubles easily than I can some of the "real" elements, and not Linc, who is a pretty believable kid turned amateur agent), it never does so enough to spoil things. There are lots of little bits of history, along with clues and dead ends and quirky characters and cool technology sprinkled along the way to make the mystery fun.
Short answer: I see no reason why this shouldn't be a great hit with its 4th and 5th grade target audience, and there's enough slightly dry wit to the writing to make it fun for older readers too.
Here's another review, at Ms. Yingling Reads, that goes into more detail about the plot.
Disclaimer: review copy received from the author