The Mendelssohn Octet on a summer’s evening, a short walk away down the river to the old Divinity School, takes a lot of beating for sheer enjoyment. And it was excellently played last night with verve and obvious relish — after some (Richard!) Strauss and Shostakovich — by the young 12 Ensemble. The audience rightly loved them: if you get a chance to catch them in concert, do so! Meanwhile, here they are with the first movement of the Octet from an Oxford concert last year.