To label George Friedrich Handel's opera "Teseo" a neglected gem is a rather gross understatement. The third of the so-called "London" operas, churned out as the prolific 28-year-old German composer was just becoming the toast of that merry olde town, "Teseo" premiered at the Queen's Theatre in the Haymarket in 1713, enjoyed a successful, if somewhat problematic run -- and dropped out of the repertoire for 234 years!

It resurfaced in Göttingen, Germany, in 1947 but really got its boost back into favor with observances of the Handel tricentennial in 1985. Now the Bay Area's shining exemplar of period orchestras, the Philharmonia Baroque, whose music director, Nicholas McGegan, conducted one of those 1985 revivals in Boston, is dusting it off for a run next week in Atherton, San Francisco and Berkeley.

The opera's titular character is the Theseus of Greek legend -- the war hero who clobbered the Minotaur in the labyrinth, as you'll doubtless recall. Soprano Amanda Forsythe will be filling that "pants" role in the new production.

But all of the heavy action -- and much of the fiercest vocal theatrics -- revolve around that most vengeful of sorceresses, Medea, she of the feed-the-children-to-the-faithless-husband fame, who has come, in this opera, to Athens to put that ugly past behind her. Alas, as the gods would have it, peace, love and understanding are not to be hers.

The formidable soprano Dominique Labelle, a favorite of the Philharmonia Baroque, sings the role of Medea, who has been promised betrothal to Teseo/Theseus by King Egeo in return for her wizardry on his behalf during wartime. But Teseo loves the princess Agilea, the unfortunate object of Egeo's romantic ambitions. And the plot, as they say, thickens, with much conniving, deception and desperation emanating from Medea.

Soprano Amy Freston sings the role of Agilea, who is Medea's foil in just about every aspect -- loyal, faithful, kindhearted, pure, etc. Countertenor Drew Mintner is Egeo, and soprano Celine Ricci and countertenor Robin Blaze are Clizia and Arcane, respectively.

The opera will be semi-staged in costume and conducted by McGegan, sung in Italian with English translation provided.

Details: 7:30 p.m., April 10, at the Center for Performing Arts in Atherton; 7:30 p.m., April 11, at the Herbst Theatre in San Francisco; 7:30 p.m., April 13, and 4 p.m., April 14, at First Congregational Church in Berkeley. Tickets, $25-$100, are at 415-392-4400 or www.cityboxoffice.com.

A COLLABORATION CONTINUES: Pianist Anne-Marie McDermott, a longtime colleague of Nadja Salerno-Sonnenberg, is amid a four-concert run with the violinist and music director of the New Century Chamber Orchestra. She is the guest soloist for the Mozart Piano Concerto No. 12 in A major, with remaining performances at 8 tonight at Berkeley's First Congregational Church, 8 p.m. Friday at Palo Alto's First United Methodist Church and 5 p.m. Sunday at the Osher Marin JCC in San Rafael. McDermott also participates in the Concert for Violin, Piano and String Quartet by Ernest Chausson, a Romantic piece of French origin usually described as a violin-piano duet with string quartet accompaniment, played by the entire 19-member NCCO string ensemble for these concerts. Composer Osvaldo Golijov's "Last Round," written as a tribute to tango master Astor Piazzolla, completes the program. Tickets, $29-$59, are available at 415-392-4400 or www.cityboxoffice.com.; more information at www.ncco.org.

IT'S A GOODE THING: Eminent pianist Richard Goode makes his debut appearance on the Chamber Music San Francisco schedule at 8 p.m. Saturday with a recital of late works for keyboard by Beethoven at the Herbst Theatre. His program includes the sonatas in E major, Op. 109; A-flat major, Op. 110 and C minor, Op. 111 and the Bagatelles 6-11 from Op. 119. Tickets, $40-$55, are at 415-392-4400 or www.chambermusicsf.org.

IN ACCORD AGAIN: Now that the San Francisco Symphony and its striking musicians have come to a tentative agreement, this weekend's concerts with guest conductor Bernard Labadie, soprano Lydia Teuscher and tenor Nicholas Phan are back on schedule. The program: Mozart's "Ave verum corpus" and Symphony No. 39 in E-flat major and Handel's "Ode for St. Cecilia's Day," featuring the vocal soloists and the S.F. Symphony Chorus. Tickets, $37-$150, are at 415-864-6000 or www.sfsymphony.org.

Contact Sue Gilmore at sgilmore@bayareanewsgroup.com