The study aims to gain a better understanding of a doctoral mobility programme “Kristjan Jaak” initiated by the Estonian government. Doctoral candidates are an increasingly international group, indispensable for both sending and receiving countries. Their mobility is essential for raising the quality of higher education in sending countries but entails a risk of brain-drain. Following the premises of a realist evaluation approach, the overarching research question of this study was “what is it in the Kristjan Jaak programme that works, for which participants, in what circumstances and why?” The data was collected using the documentary analysis, realist interviews and observation. A thematic analysis, in combination with statistical analysis, was conducted iteratively throughout the data accumulation process. The findings emphasise the importance of understanding the contextual circumstances that by activating different emotional and behavioural mechanisms lead to expected and unexpected outcomes. Five themes emerge from the analysis. First, strong professional contacts with colleagues at home before and during the studies abroad nourish the feelings of belonging and acceptance, making it the most reliable instrument to secure graduates’ return and integration. Second, lack of flexibility and consistency in requirements undermines students’ satisfaction with grant provisions and their gravitation towards home. Third, the long-term mobility programmes should aim to equip participants with knowledge, relations and skills necessary for the impact at home. Fourth, start-up and post-doc grants are weak return facilitators, although central for independence and career progress of returnees. Fifth, like-minded colleagues and resources are required to achieve professional fulfilment and impact after the return. Causal patterns behind various programme outcomes disclose more nuanced knowledge of return mobility determinants.