A few weeks ago, at the very un-rock-and-roll hour of 6:30 p.m., fans crammed into a Boston club -- long before headliners, Thursday and Thrice, took the stage -- to crowd surf and scream lyrics in unison with rock's unlikeliest up-and-comers, Coheed and Cambria. Lead singer Claudio Sanchez sported a 'fro of heights not seen since the heyday of Bone Thugs-N-Harmony and performed such piercing vocal acrobatics as are frequently heard only from the mouths of Rush's Geddy Lee or Justin Hawkins of the Darkness. His quartet hammered out tunes that followed the adventures of two characters inhabiting a nightmarish universe. Yet there was nothing jokelike or reminiscent of Dungeons & Dragons about the quartet's pummeling meanderings through prog-emo, math rock, low-end skronk, and even hair metal -- either onstage or on the band's sophomore opus, In Keeping Secrets of Silent Earth: 3. The second installment of a planned trilogy of albums, Secrets ups the pretension quotient with song titles such as "The Velourium Camper I: Faint of Hearts" -- and, at 70 minutes, retains the bloated grandiosity of concept albums crafted by arena stalkers of the 1970s. Inexplicably, though, the disc is an unqualified success, thanks to its wildly imaginative imagery and ability to lure listeners into its gruesome world and still leave them clamoring for more.