Let us borrow a phrase from our English cousins," begins the distinguished speaker at Manhattan's Lotos Club. Holding his claret aloft, he bows toward a frail, bearded figure at the head table and intones: "Long live the Queen!" The packed room bursts into applause. The toast, of course, was meant not for Queen Elizabeth II but rather for some Yankee royalty: mystery author Ellery Queen, whose reign has now stretched to 50 years. To celebrate the semicentennial, the first four Queen novels have been reissued, and a shy septuagenarian is emerging from behind the famous pseudonym.

As befits someone often hailed as America's greatest detective writer, Queen is a mysterious fellow. For starters, he is both author and main character (although the books are written in the third person). Furthermore, Queen, the writer, is not one person but two: Frederic Dannay and Manfred B. Lee. And carrying the mystery one step farther, Dannay and Lee are first cousins who were born Daniel Nathan and Manford Lepofsky.

"I'm a very lucky guy," says Fred Dannay, 73. "There aren't many writers who are around to celebrate their first book's 50th anniversary." Sadly, the small (5'5½"), owlish author is celebrating without collaborator Lee, who died of a heart attack in 1971. "We had two different personalities," says Dannay, "which, with some strange chemistry, combined to make a single person." Indeed, though Dannay still edits Ellery Queen's Mystery Magazine, he has yet to publish a novel on his own. "There is something in progress," he says, mysteriously. "But I don't want to talk about it."

The two halves of Ellery Queen were born nine months and five blocks apart in Brooklyn. Dannay and Lee were boyhood pals. "It was more than friendship and more than first-cousinship," says Dannay. "It was perfectly natural that the two of us should collaborate." They got their chance in 1928. Dannay had dropped out of high school to help support his family as a copywriter and art director in Manhattan. He lunched with his cousin, who wrote publicity, every day. When McClure's Magazine and a publisher offered a $7,500 prize for a work of mystery fiction, the two young men decided to try to write a story together. Appropriately, The Roman Hat Mystery was cooked up in an Italian restaurant, and the 43-year partnership went on to produce 63 novels, seven collections of short stories and 100 anthologies.

Dannay feels that some of Queen's popularity derives from his memorable name. (He changed his own to Frederic because of a fondness for Chopin; Dannay is a combination of the first syllables of his original name.) Ellery was a schoolyard friend, and Queen was chosen because it was euphonious. "We were so naive," laughs Dannay, "we had absolutely no idea that 'queen' had another possible meaning."

Frugality forced them to share hotel rooms and train compartments when on lecture tours during the '30s. They flipped a coin to see who would be Ellery Queen. (The other was Barnaby Ross, another nom de plume they used for four books.) To keep their true identities secret, both wore masks.

Dannay is still secretive about whodunwhat in concocting their mysteries. "There isn't a method conceived or invented by the mind of man," he says, "that we didn't try at one time or another." They sweated in the same room, in different rooms, over one typewriter or two, 3,000 miles apart (by phone) or just 50 miles. "We were collaborators, but we were also competitors," reveals Dannay. "We were always trying to top each other, and the result was a quality and sharpness that we couldn't have achieved otherwise."

The twice-widowed Dannay lives in the New York suburb of Larchmont with his third wife, Rose. She didn't know his true identity when they met at a dinner party three years ago. "So he knows I didn't marry him for his money," she laughs. A diabetic, Dannay now watches his diet and relaxes in front of the TV ("I can watch the worst stuff and enjoy it") or pores over his valuable first editions of poetry. (His collection of 6,000 mystery books was sold to the U of Texas in 1958.)

Ellery Queen started as a "one-book lark," but now Dannay aspires to be the world's oldest mystery writer. His plot is simple. "You shouldn't retire," he declares, "because you'll either die or fade on the vine. I intend to keep ongoing."