Running unnecessarily long at over two hours, Two Sisters is an uneven combination of tragedy (three actors, a chorus, and rough unities of time, place and plot), comedy, sentimentality and formal experimentation. As his first ‘original work to be staged at the Lyceum’ since playwright David Greig became the theatre’s artistic director in 2015, it places his comprehensive theatrical knowledge at the service of a plot that, ultimately, sheds little light on its themes of midlife crisis, nostalgia and the optimism of youth.

Powerful performances from Jess Hardwick (Emma) and Shauna Macdonald (Amy) lend the titular siblings a sympathetic dynamism, as they revisit a childhood holiday park and mull over the disappointments of adult life. A chorus of young people, in the script’s more experimental turn, read the audience’s answers to a questionnaire about youthful memories, providing an ironic perspective on the sisters’ bickering and fond recollections of music and teenage romance. On the downside, it also interrupts the dramatic flow which gently studies a potential love triangle and the acceptance of responsibility.

Setting the action at a dilapidated caravan resort, Greig speaks to the young summers of adolescence and a strange mixture of listlessness and potential. Yet the conflict between Emma and Amy is based on a generic sibling rivalry and resentment, and they fail to rise above stereotypes of the respectful and the wayward woman. Greig’s sympathy for the characters prevents his script from descending into either tragedy or condescension, but this is an amiable and wistful meditation that lacks a forceful resolution.

Two Sisters, Lyceum Theatre, Edinburgh, until Saturday 2 March.