Sir Walter is in fact Wobbler, he was trapped in the past when the butterfly effect occured. Jonny, Kirsty and Yo-less return to the past to try and put things right and rewrite history so Jonny is born and Wobbler can return to the present.
Jonny, Kirsty and Yo-less make it back from the 1940s, but Wobbler and Bigmac are still there. To make things worse the mysterious Sir Walter turns up and talks about the ""butterfly effect"", basically: little things in the past have big consequences. To