This book. Is one of those books you (I, anyway) pick up thinking, "eh, not really my kind of thing, but I'll take a look."
Then you get carried on a wonderfully enjoyable ride, resenting when you are forced to tear yourself away to deal with the real world, and googling the author's name the second you finish the book, to see what else she has written.
"When Earth comes under attack by aliens, hilarious heroine Alice Dare and a select group of kids are sent to Mars. But things get strange when the adults disappear into thin air, the kids face down an alien named Ths, and Alice and her friends must save the galaxy!