Having revealed in Mac B., Kid Spy Mac Undercover (2018) that, long before becoming a world-famous writer, he was a secret agent for the Queen of England, Barnett opens his casebook again is time to solve a classic locked-room mystery. It seems that Her Royal Highness has received an unsigned letter threatening justice for an old grievance, and she naturally assumes that the Crown Jewels are in danger from a descendant of Colonel Blood, who tried to steal them in 1671 (this part, at least, is actually true). When indeed the scepter, orb, and crown vanish from a Tower lockup, despite the vigilance of Mac and surly beefeater Holcroft, it's off to Ireland in search of the (presumed) culprit. Almost every page contains Lowery's illustrations, loosely drawn and garishly colored in green and orange, which give the whole affair a zany feel that is much enhanced by the narrative with its running gags. Kudos to a pint-size Poirot, pre-Mustache! (2011).

Child spy Mac (Mac Undercover) quickly finds himself in the middle of a "howdunit" when the Queen of England's Crown Jewels are stolen from right under his nose. Barnett's signature dry wit and snappy back-and-forths keep this second offbeat installment steadily moving forward; Lowery's cartoony spot art in black, green, and orange provides additional historical and cultural information and frequently supports the narrative.

This young spy does not suffer from the sophomore slump!Barnett and Lowery team up again in this second outing of international espionage mystery with royal overtones. In 1989, the queen of England once again calls on young Mac after she receives a letter threatening the theft of the crown jewels. Neatly interwoven with Mac's caper is the true story of Col. Thomas Blood, a 17th-century thief of the aforementioned jewels. Barnett combines mystery, riddles, a lot of humor, an engaging first-person narration, and nostalgia for all things 1980s into a (mostly) smooth whodunit for young readers. Readers of Chris Barton and Don Tate's Whoosh! (2016) or kids who've written a report on Lonnie Johnson will notice one anachronism: The Super Soaker may have been invented in 1982, but it was only released in 1990 and branded under that name in 1991. Lowery's believably childlike cartoons, done in black and white with bright yellow and green highlights, are amusing but don't always correspond with the text (partly due to this color choice, explained in a prefatory note young readers might well ignore). Quibbles aside, this is a nifty mystery for young readers and a worthy sequel to the first. Here's hoping No. 3 will get all the details right and add some characters of color to diversify the white-presenting cast.This romp will definitely find an audience. (Mystery. 7-10)