"Bitter" may be the first word spoken in Yasmina Reza's ruefully comic strangers-on-a-train duet, but the lasting aura is of disarming geniality. Reza's text, as translated from the French with characteristic mellifluousness by Christopher Hampton, makes superb fodder for Spare Stage cofounder Stephen Drewes' mission-specific presentation: All it requires are two people, two benches, and two pools of light. He is a weary, aged novelist, and the author of the book she happens to have in her purse; she is the thoughtful, loyal reader he's always wanted and never really expected. En route from Paris to Frankfurt, they take turns talking to themselves, spilling banalities and profundities alike from parallel streams of consciousness, and we wait for the golden moment when finally they'll talk to each other. Ken Ruta and Abigail Van Alyn, both quite obvious veterans of intimate dramatic simplicity, make as much with silent moments as they do with their respective inner-life soliloquies. Their choices seem singular and organic enough to elasticize the play's conceptual austerity. Bitter it isn't, but instead highly gratifying — both a literary and a theatrical affirmation.