What is the main conflict in Light a Penny Candle by Maeve Binchy?

The story follows follows two families, one English and the other Irish, through a period of twenty years (1940-1960). The families are first entwined when Elizabeth White, at age ten, is sent to Kilgarret, Ireland, to escape the German bombing of London and is adopted for five years by the O'Connors, whose daughter Aisling is also ten. Linked only by letters for most of the novel, as they mature and each find tragedy in love, Elizabeth and Aisling are reunited towards the end in London where, both widowed, they resolve to begin life again together.