We know the “immortal” George Bernard Shaw – playwright, pacifist, critic, vegetarian. But, really, what made him tick? And who was Mrs. Campbell? She was a famous Gilded Age actress on par with Eleanora Duse, Elen Terry, and Sara Bernhardt, who played lead roles on the London stage and whom Shaw cast as Eliza Dolittle in his Pygmalion (My Fair Lady). Shaw and Campbell fell “violently” in love with each other, even though both were married at the time. Based on hundreds of intimate, exquisitely personal letters they wrote to each other from 1912 to 1940. “Mrs. Campbell! Mr. Shaw.” is a historical record of a bygone era, one that echoes the timeless and universal joys and sorrows of middle-aged people growing older, and perhaps wiser – wise enough to poke fun at themselves and the world. Drawing from the epistolary form, the play interweaves snippets from Shaw’s plays with the letters. The effect is an even and entertaining match of outsized personalities by turns that are comic and tragic.