Rock 'n' Roll isn't one of Tom Stoppard's great plays (it's no Arcadia or Rosencrantz and Guildenstern Are Dead). But a merely good Stoppard still beats almost anyone for wit, intelligence, and the sticky warmth of human relationships. It begins in Oxford, 1968, as a Czech PhD student runs home after the USSR has invaded his home country. The play ping-pongs between London and Prague, fusty British Marxists and Czech longhairs who just want to make "socially negative music." Plus: sex, drugs, and you-guessed-it. The excellent cast (especially Anne Allgood as a cancer-stricken professor of Greek) elevates the script from merely good to glowing. (ACT Theatre, 700 Union St, 292-7676. 2 and 7:30 pm, $10–$55. Through Nov 8.)