Drawing on data from the megalithic tomb in Resmo on oland in the Baltic Sea, we use a multi-isotopic approach, involving the systematic treatment and modelling of extensive human and faunal isotopic data (C-14, C-13, N-15, S-34 and Sr-87/Sr-86), along with archaeological contextual evidence, to study change and interaction. The fact that people utilize aquatic resources necessitates modelling of the sulphur and strontium isotope data, to prevent the aquatic contribution from obscuring the local terrestrial signal. It was possible to demonstrate how the people buried in Resmo went through dynamic changes in diet, mobility patterns and cultural identity during more than two millennia of burial practice: from the incipient farmers of the Funnel Beaker Culture, through the cultural encounters and transitions during the Middle Neolithic, to the newcomers furthering intensified agriculture, trade and metal craftsmanship during the Bronze Age.