The armchair guide to Mad Men

The advertising-agency drama returns for its fifth season next week. Already lost the plot? Will Dean, author of the definitive book on the show, brings you up to speed

If you've ever watched the Sixties ad-industry drama Mad Men, which returns to UK screens on Tuesday, you'll know that's it's a rich, deeply layered period drama of lovingly detailed proportions. If you've never watched it, you're probably sick of hearing it described in such luminous terms. But, tough, it is that good.

Its four seasons and 52 episodes have so far covered the travails of staff at the New York ad firm, from mystery pregnancies to alcoholic breakdowns right through to divorce, rape, racism and the occasional spot of happiness.

All these dramas, centred around the tumultuous life of ad executive Don Draper (Jon Hamm) and his colleagues and family are coloured by contemporary happenings from the early Sixties, whether it's the typing pool being left in tears at the news of Marilyn Monroe's death; Don blagging Beatles tickets for his daughter; or Roger Sterling's daughter's wedding being ruined by the murder of JFK.

Indeed, one of the great joys that accompany a new series of Mad Men alighting on our screens is speculating as to which socio-cultural events will impinge of the world of Madison Avenue.

Secrecy about the new series is currently at a Pentagon-like level, but an email from the drama's creator, Matthew Weiner, to journalists about a Dusty Springfield song used in episode one suggests that the new series is set in early 1967. So what can we expect? A teenage Sally Draper running off toSan Francisco to join in the summer of love? The increasingly liberal Pete Campbell and his wife, Trudy, to join in anti-Vietnam and anti-racism protests like the Central Park Be-In?Or just subtle nods to some of the year's most famous events, which include Muhammad Ali refusing military service, the release of Sgt. Pepper and the US race riots. or just a full-cast singalong to Engelbert Humperdinck's Release Me? Maybe not.

Whatever is referenced, one of the best things about Mad Men is finding out what everything – from background TV reports to the song playing in a nightclub scene – means and relates to. It's a show that rewards extra-curricular digging.

The plots are equally dense, too. There's so much happening in Mad Men – despite the unfounded regular criticism that 'nothing happens' – that it's easy to forget where we're up to. Or,if you've not seen it all, even easier to be baffled by. Hopefully this cut-out-and -keep graphic, which shows who's who at Sterling Cooper Draper Pryce and how they connect to Don Draper, will help.

Mad Men starts with a double episode at 9pm on Tuesday, Sky Atlantic. Will Dean is the author of The Ultimate Guide to Mad Men (£8.99)