With the widest catchment area of any river in Britain, the Tay drains much of the lower Highlands of Scotland. A vast network of lochs and smaller bodies of water feed the rivers Isla, Garry, Tummel, Almond and Earn, which all in turn flow into this mighty river as it cuts its way through the landscape. Robin Crawford has a very personal connection to this river, and as he walks along its banks, from its source on Ben Lui until it spills into the North Sea at Dundee, we find parallels between his own experience and the broader history of the Tay. Reaching back to a prehistoric fish found near Balruddery in Perthshire, we follow its story through time to the present day, with detours to seek gold, clans, battles, forts, disasters, witches and whisky en route. In amongst this broader sweep of history is Robin's own story. As he walks, he reminisces and reflects on the small moments of a life on which events turn.