The advent of the Internet has been instrumental in producing new Game Based Learning (GBL) tools where education and games converge. Alternate Reality Games (ARGs) are one such GBL tool. Interactive narrative games that use the Internet as a central communications platform, ARGs challenge players to collaboratively collate a fragmented story. When used for educational purposes, Serious ARGs provide a novel form of GBL that encourages critical thinking, develops problem-solving skills and fosters collaborative learning. However, the pedagogical application of ARGs is still relatively new. This article presents a background to ARGs and Serious ARGs. It also outlines the lessons drawn from Plunkett's Pages, a Serious ARG that focuses on actual historical events. A selection of evaluation criteria, extracted from the reflections of those who played Plunkett's Pages are presented. These criteria are intended to enable novice ARG designers or educators to formatively evaluate an emerging ARG design.