The Door in the Alley by Adrienne Kress

Sebastian loves to follow rules and always does his best to please his parents and his teachers.  Then one day he sees a door in an alley and a pig with a little hat that intrigue him.  Meanwhile, an orphaned girl, Evie, is enduring another dinner with two of the most boring people Evie could imagine, when they are attacked by some frightening thugs.  Right before the house she is in explodes, one of Evie's hosts gives her a letter from her grandfather whom Evie thought was dead.  The letter is a cry for help.  Both Evie's letter and the pig with the little hat lead the two children to the Explorer's Society, a mysterious organization that holds the key to finding Evie's grandfather.

This was a fun and lighthearted adventure with kid appeal.  Kress's writing is quirky and has a lot of personality and humor.  Sebastian and Evie are likable characters as are the unique adult members of the society.  Of course, this is the first in a series, and it is entertaining enough I might read the next. (2017, 305 p.)