So many have departed but O'Brien still has six in Derby

Ballydoyle's line-up for Saturday's Classic underlines the depth of their riches

And then, rather like characters in an Agatha Christie novel, there were six. From an original entry of 70 un-named yearlings in December 2007, reduced to 35 in March this year and further whittled to nine last week, the Ballydoyle challenge for the 230th Derby was announced yesterday as a sextet. After the dust settled on a crucial test-drive session on the Co Tipperary gallops, Aidan O'Brien confirmed Fame And Glory, Rip Van Winkle, Black Bear Island, Masterofthehorse, Age Of Aquarius and Golden Sword as his squad for Saturday's £1.25m Epsom showpiece.

Six jockeys were named, too, though punters must wait for the decision on who rides what. The Derby contenders will have one more piece of fast work; the weather and likely ground conditions and any other runes will be analysed. And after stable No 1 Johnny Murtagh has made his choice, his rejects will be divvied up among in-house men Seamie Heffernan and Colm O'Donoghue and outsiders Pat Smullen, Ryan Moore and Richard Hughes.

The last horses crossed off the list were Malibu Bay, bound for the Prix du Jockey-Club a week today, and Royal Ascot-bound Freemantle and Johann Zoffany. Those of the team's aspirants who fell by the wayside earlier include Cool For Cats, who cost $1.7m as a youngster, million-guinea purchase Yankee Doodle, and Aristocrat with a 750,000gns price-tag. But all losses will be recouped if O'Brien produces a third Derby hero to stand at Coolmore stud alongside Galileo and High Chaparral.

Some say the Derby is a fading glory, an irrelevant anachronism, but top professionals say otherwise and the cast of classy equine characters who will assemble on the Downs for the best day of the sporting year must answer a series of intriguing questions.

Can Sea The Stars, vying for favouritism with Fame And Glory, become the first since Nashwan 20 years ago to add the Derby to his 2,000 Guineas? Can High Chaparral's full brother Black Bear Island become the first in 109 years to follow in a sibling's hoofprints? Will O'Brien's scattergun attack prove more effective than the sniper strategy of John Oxx, with Sea The Stars, or of Jim Bolger, with Gan Amrhas? Will Murtagh get it right? Could it be an outsider's year, perhaps a first Derby for the Godolphin blue through Kite Wood, or a first Classic for Mick Channon, through Montaff?

It's not at this stage a whodunnit, but a who'll do it? The clues are there but the standard-bearer for a generation will not be identified until his pace, balance, stamina, acceleration and resolve pass muster over Epsom's switchback mile and a half. Of those who go onto the roll of honour, some can hack it at the top afterwards some can't but that is the point of the Derby; the race is a beginning, not an end.

Friday's Oaks, the distaff equivalent over the same challenging track, will be a maximum of 12-strong and in contrast to the Derby, the betting indicates the prize will stay at home. The Newmarket-trained Sariska (Michael Bell), Rainbow View (John Gosden), Midday (Henry Cecil) and Phillipina (Sir Michael Stoute) head the market, with the sole Irish raiders Perfect Truth (O'Brien) and Oh Goodness Me (Bolger) after the defection of Again and Beauty O'Gwaun at yesterday's penultimate confirmation stage.

Last year's Oaks winner Look Here will take on the boys, including Youmzain, Frozen Fire and Casual Conquest, in the Coronation Cup on the same card. But America's star filly Rachel Alexandra, who beat colts in the Preakness Stakes, has declined a second clash with her Pimlico victim Mine That Bird, the Kentucky Derby hero, in Saturday night's Belmont Stakes. Her absence leaves rider Calvin Borel free to rejoin Mine That Bird in his bid for all three legs of the US Triple Crown.

On yesterday's domestic programme, the most impressive performance came at Haydock, where the Oasis Dream four-year-old Main Aim took the step up from handicap to Group Three company in his considerable stride, quickening clear under Ryan Moore to score by two lengths. Sir Michael Stoute's charge now has the top level, possibly Royal Ascot's Golden Jubilee Stakes, in his sights.

The award for gallantry went to 12-year-old Caracciola, who belied his years to thwart Friston Forest by a short-head at York. And the afternoon's most appropriate winner was also at Haydock; Ialysos, an import from Greece, took the Achilles Stakes.