On a cross-country vacation with their parents, twins Coke and Pepsi, soon to be thirteen, fend off strange assassins as they try to come to terms with their being part of a top-secret government organization known as The Genius Files.

"Twelve-year-old twins Bickford and Rebecca Kidd and their two older siblings travel to Africa to track down priceless artifacts that will keep the family's treasure hunting business afloat long enough to rescue their kidnapped mother--and possibly find their missing father"-- Provided by publisher.

"Tween twins Coke and Pepsi McDonald have finally reached the last leg of their wacky and dangerous cross-country road trip, but they must fend off a host of strange assassins before they reach their home in California"--

While in Scotland visiting relatives, thirteen-year-old twins hunting for ghosts in an old cemetery find big trouble when Peter is possessed by the spirit of a man who is determined to keep his twin sister from the man she loves.

"While visiting Alaska, Ethan and Ella follow some icy paw prints that lead to a brand-new mystery"--

Twins Stephanie and Zeke, their friend Hector, and cats Fitz and Meathead once again venture into the world of Underwhere, this time looking for the missing Brush of Wisdom, a magical item that looks suspiciously like a jewelled toilet brush.

Hmong American twins Astrid and Apollo and their father are excited to start their relaxing ice fishing expedition, but freezing Mom is worried things could go wrong, which they do--sort of.

Astrid, Apollo, Eliana, and their parents are at the state fair and enjoying a scavenger hunt based on the five senses, but none of them can figure out what it is that little Eliana wants.

When Zeke, his twin sister Stephanie, their neighbor Hector, and Hector's cat Fitz slide into the world of Underwhere, Zeke is hailed as a prince who will, according to an ancient prophecy, free the Undies from the evil UnderLord's rule by finding and destroying his throne.

While visiting relatives in Scotland, three children come to the aid of a refugee from the distant past, a young Pict girl escaping a massacre of her people.