"DEAR child..." and there's a genial warmth in Tam Dean Burns' voice that wraps round the wee ones from Sorn Primary school like a welcoming hug.

We're sitting in the afternoon daylight that's flooding in, unhecked, on an event that could be described as a tad "hand-knitted", but for the weeks of thoroughly sophisticated thinking that has gone into this National Theatre of Scotland (NTS) project.

This touring production of Harry Horse's whimsical, but pithily nuanced children's book about global warming and endangered species has been put together with an eye to travelling (carbon) light: and so the set is little more than a fold-over backcloth, props are minimal – and it can all be packed down into trailers that the company will tow behind their bikes as they ride from place to place. "Dear child..." Director Joe Douglas's adaptation relishes the style of Horse's original with Grandpa (Dean Burn) describing his eccentric, improbable adventures in vivid, pawky letters to a much-loved grand-child. In The Last Polar Bears, this indefatigable codger, with his bolshy-mouthy dog Roo (Kirstin McLean, with a life-size cut-out puppet) – and Joyce Falconer as just about everyone else – heads to an Arctic that is melting and vanishing. The letters make fabulous, rambunctious work of deeply concerning, serious issues. But more than that, there is the hint that Grandpa too, might be nearing an end – a prospect handled with a delicate ambiguity by Douglas and his tremendous cast. Dean Burn, especially is a twinklingly roguish Grandpa who finds, not polar bears, but happiness in an imagined paradise of ice-cream-topped mountains. Young and old, we melt into heart-felt applause.

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