Andrew and Evie aren't initially sure what to make of the package that arrives at their door soon after they move to a new town. It's filled with random things--a key, something that looks like a kaleidoscope, a seed packet, and a cryptic note. But over time, each item takes on unique importance.

The twins decide to fill the dull weeks before the start of school by spying on their neighbors. Their first target is their next-door-neighbor. At first she seems like a run-of-the-mill older lady, but she turns out to be a retired code specialist. She teaches them to create and break codes, skills that become important as twins' search for their mother intensifies.

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Evie and Andrew have always wondered what happened to their mother after she disappeared on their birthday. Now they are starting to find out . . . and the results are very surprising. Their mother was into something big, and now the twins are being drawn in as well. Nobody - not their baby-sitter, not their new school friend, not a pair of menacing bikers - is who he or she appears to be. But Evie and Andrew will have to uncover the truth if they ever want to see their mother again.

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It's been almost a full year since Andrew and Evie's mom disappeared, and the twins are determined to find her. They've been following her trail, decoding the clues she's left them. And that trail is drawing them closer to their mother than ever before.

But now the Company is on to the fact that Mom is communicating with the twins - and they'll do anything to get to her first. The Company's agents are desperate to intercept Mom's messages. It's up to Andrew and Evie to stop them - and to find Mom before her enemies do.