When Dan realises someone new will be moving in next door, she isn't sure what to expect. She certainly isn't expecting the adventure she and her twin brother, Dom, are about to be swept into. Myrtle Marple might seem like an average old lady at first but there is much more to her than meets the eye. With the incredible technology she possesses, Dan and Dom might just be in for the most exciting summer yet. But the twins aren't the only people interested in Myrtle's technology. Will Dan and Dom be able to help their newfound friend beat the bad guys and make it home safely before their parents even realise that they're gone?