Portals are two a penny these days: wardrobes, looking glasses, giant peaches, the back of a 7∏th-floor filing cabinet, all these have served. In this S4C Films production, three (live action) teenagers take a dive into the aura of an underwater island off the Welsh coast, and find themselves filling the boots of animated characters in a retelling of the Four Branches of the Mabinogi. There are catchier ways to time travel, but it's an intriguing destination. Medieval Welsh folk myths of an Arthurian stripe, the Mabinogion - the 'Four Branches' provide their core - unfold tales of courtly romance and intrigue, clan strife and black magic. There's far too much narrative to annotate here; too much, indeed, to pack convincingly into a 90-minute feature. The screenplay whisks through sagas of several lifetimes with judicious concision, but the pace never quells enough for any relevant morals to cohere. The animation (essentially 'realistic' 2-D cell-style, with licks of 3-D CGI and some less persuasive photo superimposition) has a well worked, perhaps aptly antiquated quality. The 12A certificate is for a touch of sex and some lusty violence.