The five-CD UFO box set The Chrysalis Years (1973-1979) chronicles the recordings that represent the British rock group's artistic and commercial peak. It's an era that corresponds exactly to the tenure of guitarist Michael Schenker, who joined UFO founding members Phil Mogg (vocals), Pete Way (bass), and Andy Parker (drums) after they had made two studio albums and a live disc with original guitarist Mick Bolton, and left after five more studio albums (Phenomenon, Force It, No Heavy Petting, Lights Out, and Obsession) and another concert collection (Strangers in the Night). Unlike the first three LPs (which were not released in America at the time), five of the six records with Schenker made the U.S. Top 200 chart, with Lights Out reaching the Top 30, while the band's early space rock style gave way to a hard rock sound that earned comparisons to the Who and Led Zeppelin. The Chrysalis Years (1973-1979) contains the complete contents of those six albums, plus an entire concert performed on the Phenomenon tour at the Electric Ballroom in Atlanta; an appearance with Bob Harris of the British TV show The Old Grey Whistle Test around the time of Phenomenon; a radio session with DJ John Peel around the time of Lights Out, and assorted tracks from singles. The German Schenker, who joined as a teenager, remains the phenom of Phenomenon, as well as the rest of the music, combining the blues attack of Jimmy Page with anticipation of the fast playing of followers like Eddie Van Halen. His talents are on display as early as an extended solo in "Rock Bottom" on Phenomenon, the first of four versions of that song in the box set, and he demonstrates how lyrical he can be on the acoustic ballad "Time on My Hands" from the same LP. Most of the material beyond the regular LPs comes toward the beginning, with the Electric Ballroom show (played before an enthusiastic, if apparently sparse crowd) particularly notable, with its eight-and-a-half-minute reworking of John Lennon's "Cold Turkey." As of No Heavy Petting, keyboardist Paul Raymond had joined, and the similarities to the Who and Led Zeppelin had become overt (along with occasional nods to Bad Company and Queen). The string-laden Lights Out continues to sound like UFO's best work, with Obsession also accomplished and Strangers in the Night a victory lap. There may have been a UFO before this period, and there has been one, off and on, since, but this lengthy collection presents the band at its best.