A projectile toilet spells danger-and mess-for Area 51 and its residents.Sky Patel-Baum has had a lot of firsts since moving from boring California to Area 51. The latest first: Her alien bestie's long-lost (read: assumed dead) parents come to visit via UFO with a surprise little brother in tow. Complicated family dynamics abound, and the interstellar visitors warn that the Arthogus (an exiled alien species) are in cahoots with someone on the base to exact their revenge. Their method of destruction: launching a poop-filled space toilet at Area 51. The odds of survival? 13.875%. But who could the double agent be? Sky and friends team up once again to get to the bottom of the latest mystery-and flush the intruder out. Buxbaum's second series entry one-ups its predecessor in ridiculousness, including a bounty of fart puns. The first-person narration allows Sky's infectious personality to shine. Well-placed clues and red herrings help keep the mystery fresh while expanding the setting. The pseudo "Scooby-Doo gang" welcomes a new member in talented hacker Gertie, an astronaut's daughter. Naidu's black-and-white cartoon illustrations effectively punctuate jokes and offer occasional helpful asides. Characters are drawn in a range of skin tones; Gertie reads Black. Another cliffhanger ending makes a key revelation in addition to hinting at the next installment.Out-of-this-world potty humor with heart among the toots. (recipes) (Mystery. 8-12)