About a third of the way through One More Kiss, his new history of musicals of the 1970s, Ethan Mordden asks, a little plaintively: "Remember when musicals were about how Adele Astaire couldn't get married till the stolen jewels were recovered?" If you can, you're either a lot older than Mordden or, like him, a heck of a musical historian. But this fleeting evocation of Funny Face points up something major that went wrong with the form in the tumultuous '70s: Musicals weren't fun anymore. They grew smarter, more realistic, more ironic, more penetrating, but less beguiling. It was a fascinating, frustrating decade for the musical, and Mordden characteristically views it from every angle imaginable.

One More Kiss (Palgrave Macmillan, $27.95, 264 pages) is the latest volume in the author's decade-by-decade examination of the form from the 1920s to the present; a '30s history, Sing for Your Supper, is on the way. The '70s book definitely benefits from the author's eyewitness accounts. A tireless researcher with an engaging literary style, Mordden has a gift for making the past come alive even when he wasn't actually there for the shows and events covered. (This talent is shared by only the best theater critics and historians -- notably Walter Kerr, whom Mordden blasts here for having a tin ear.) Since he was on hand for nearly everything in the new book, from the triumphs of Follies and A Chorus Line to the dreariness of Georgy and the creepiness of Dear Oscar, Mordden can back up his usual diligent archaeology with telling firsthand accounts. It's truly the next best thing to being there.

And there's a lot of "there" there. While the '70s were not the richest musical theater decade by a long shot, either in the number or quality of productions, the decade was astonishingly eventful -- "Here we learn why the Golden Age ended," Mordden states in his first paragraph.

Consider the Broadway musical circa 1970. The old, Rodgers and Hammerstein template is simply exhausted on the evidence of Jimmy, Look to the Lilies, and Lovely Ladies, Kind Gentlemen. The few successful rock musicals -- Hair and, soon, Godspell and Jesus Christ Superstar -- are compelling clueless producers to back anything with a beat and an electronic keyboard, even if, as with Galt MacDermot's Dude, the show is "apparently more hallucinated than written." Tone-deaf critics (even movie critics!) such as Renata Adler and Pauline Kael are becoming more influential, and their excoriation of the traditional musical is sending creative teams down blind alleys. Production costs are soaring, resulting in fewer out-of-town tryouts and more emaciated-looking musicals with small orchestras and smaller casts. Established writers, who should know better, are trying to break out of molds and are thereby sending the musical in unsuitable directions. (What gave Richard Rodgers the idea that Henry VIII had anything to sing about?)

Finally, and perhaps most damagingly, the musical is veering farther and farther from the center of popular culture. It was firmly there in the 1950s, with Broadway dominating the Hit Parade and being sampled liberally on television. In the 1960s, with the rise of rock, it began to move out of the mainstream. And now, in the 1970s, it's a cultural cul-de-sac rather than mass entertainment. While such an environment arguably helps a Stephen Sondheim flourish -- he needn't appeal to as wide a public as, say, Lerner and Loewe 20 years before -- it does nothing to nurture a healthy commercial marketplace for the musical.

What a scattershot, unwieldy era it was! Mordden takes it all in, from the oblique, intelligentsia-pleasing Off-Broadway works of Stanley Silverman (Dr. Selavy's Magic Theatre, Elephant Steps) to reactionary Broadway revivals (No, No, Nanette, Irene, Good News); from the rise of the superdirector (Fosse with Pippin, Bennett with Seesaw) to the floundering of major writers (Rodgers with I Remember Mama, Lerner and Lane with Carmelina); the ascendancy of the oft-misunderstood "concept musical" (one 12-month stretch gave us Chicago, Pacific Overtures, and 1600 Pennsylvania Avenue) to the pointless traditional-musical adaptations of serious works, usually with their original titles abbreviated into meaninglessness (Angel, Raisin).

Mordden does this with a perspicacity unusual even for him: Did you ever expect to read a comprehensive deconstruction of Smith, a fun 1973 flop with botanist Don Murray literally trapped in a preposterous musical comedy, or to revisit 1971's Soon, a rock calamity starring Richard Gere, Peter Allen, and Barry Bostwick? He includes telling dialogue from the likes of Sarava and Platinum. He plumbs beneath the surface of seemingly trite hits like Grease, and finds that they're actually about something (in this case, "the crushing of the individualist spirit in a fascism of conformity"). He visits London, where American writers were escaping Broadway's brutal economics, and finds solid showmanship in Strouse and Adams's I and Albert and even in Harold Rome's Gone with the Wind. And he looks at out-of-town casualties like Lolita, My Love and Prettybelle, concluding that these dark, probing shows weren't lacking as much as their unforgiving, matinee-lady audiences were.

Additionally, Mordden recalls largely forgotten performers who made sizable contributions: Mary Jo Catlett, Don Scardino, and Daniel Fortus seem to be in practically every other musical. He offers some surprising opinions (Stephen Schwartz's work for The Magic Show is preferable to his Pippin score; Jerry Herman invests generic song forms with character detail worthy of a Sondheim) but backs them up convincingly. And there are generous examinations of Ambassador, Gantry, and Molly. About the only Broadway musical Mordden seems to have overlooked entirely is 1978's A Broadway Musical, a one-night flop with Anne Francine and Warren Berlinger, a misbegotten Gower Champion staging, and such Strouse-Adams songs as "Yenta Power."

Of course, there's a lot of Sondheim here -- his shows dominated the decade, and he found in Hal Prince a soulmate director as determined as he to challenge old-musical ideas. Mordden sits us down in the Alvin in 1970 and reminds us just how startling Company was, its nonlinear storytelling and dissonant harmonies totally at odds with Minnie's Boys, Two by Two, and musicals of that ilk. He reappraises Follies' original book, finding it superior to any subsequent tinkerings, and explains the show's constant financial failure thusly: "The work is simply too smart for its own good." Throughout Mordden's discussions of A Little Night Music, Pacific Overtures, and Sweeney Todd, he acknowledges and refutes dissenters' complaints of "no melody." Indeed, in 1976, Pacific Overtures' "There Is No Other Way" seemed to him "the most beautiful music yet heard on Broadway."

Readers of Mordden's other musical histories know what a lively writer he is; the man has a successful parallel career in fiction, after all. As a stylist, he does have an occasional weakness for the facile. In this volume, with so many train-wreck musicals to chronicle, his standard delineation of bad musical construction is to report on misconceived staging or substandard writing and cap it off with "What?!" Also, more than in previous volumes, his prose is needlessly salty: Does it really illuminate history to describe Bob Fosse choreography as "dancing with a hard-on" or to define the concept musical as "Love Life gives Allegro a blow job?" Some of his footnotes are scholarly; others are just dumb jests, such as his revelation that Patti LuPone has a brother named Jubilation T. Corn. Also, while Mordden is a thorough musical scholar, he often seems to wallow in obscure music theory just to show off.

But these are small indulgences on the part of a musical historian whose writing is so evocative, so witty, so penetrating, and so quotable; even Mordden's photo captions are entertaining. If One More Kiss serves as a dispiriting reminder of what went wrong with musicals in the 1970s, it also documents what went spectacularly right. For those of us lucky enough to have been at the original On the Twentieth Century or Ain't Misbehavin', it stirs up endlessly pleasurable memories. For those who have long treasured the scores to The Baker's Wife and Mack and Mabel, it offers well reasoned justification. For musical theater lovers in general, it's a fast and energetic read, yet a staggeringly smart and complete one.