DD is trying to remember this book I am sure you literary geniuses will recognise it so here goes. Boy goes to stay with his uncle during the holidays. His uncle is going to Peru to find some treasure. The boy convinces his uncle to take him with him. Powerful baddies are trying to stop them. Other points are that a car falls off a cliff/is thrown off by the baddies(the characters are not in it at the time obviously!!!) any ideas?