The date is October 28, 1968.

The Mothers of Invention are playing the Royal Festival Hall in London.

Frank Zappa has booked 14 musicians from the BBC Symphony Orchestra to accompany them during the first part of the show.

He had been writing chamber music pieces in the hotel rooms he visited and wanted to try them out.

He strung them together by devising a psychodrama he called "Progress?" This was meant (and indeed turned out) to be a one-time performance, so he made sure to record it.

He released the whole thing as Ahead of Their Time 25 years later.

The first half of the disc is comprised of the "play." A faction of the Mothers want to play conservative concert music.

Don Preston advocates progress with his avant-gardist electronics.

He and pianist Ian Underwood battle it out while other frivolous characters (played by members of the Mothers) intervene.

It must have been a lot of fun to watch (and it was filmed; parts of it appeared in the movie Uncle Meat), but some of the more visual scenes translate poorly on record.

More important is the music itself, which definitely points toward the score to 200 Motels -- it even includes "Holiday in Berlin," which will eventually become a central theme of the film music.

The second half of the CD presents the rock part of that night's concert.

All instrumental and very focused, it presents Zappa's best tunes from 1967-1968, including the complete sequence that includes "Let's Make the Water Turn Black," "Harry You're a Beast," "The Orange County Lumber Truck," and "Oh No." The sound quality is far from perfect, but this is a crucial document that fans of the '60s Mothers will enjoy.