London - Usain Bolt's suspect hip and Mo Farah's status as the golden boy of British athletics will come under scrutiny when both return to London's Olympic stadium this weekend.
The two-day so-called Anniversary Games, which incorporates a Diamond League meeting, features a glittering cast but six-times Olympic gold medallist Bolt is the undoubted top of the bill when he goes in the 100m on Friday.
The world record holder has looked a long way from the unbeatable sprinter who elevated track and field above the murky waters of its dope-stained past with stunning 100m/200m doubles at the Beijing and London Olympics.
This season though he is yet to dip below 10 seconds in the 100 and missed the recent Jamaican trials with a troublesome hip injury.
Bolt's fitness, and speed will be closely monitored a month before the world championships in Beijing when American Justin Gatlin, on fire this season, will be itching to have a crack at him.
There will be no showdown in London, however, and a fit Bolt looks a strong favourite ahead of European record holder Jimmy Vicaut of France, who ran 9.86 seconds in Paris three weeks ago, and American Mike Rodgers.
With twice-banned Gatlin causing a stir in the athletics world, a sharp 100m by Bolt would be a timely PR boost for a sport still mired in suspicion - most recently allegations surrounding Alberto Salazar, coach to Britain's 5,000m and 10,000m Olympic champion Farah.
Farah has pledged his allegiance to Salazar, who is being investigated by both USADA and UK Anti-Doping over allegations that he has violated doping rules and will run the 3,000m, also on Friday.
Although there is no suggestion of any wrongdoing by Farah, it has been an uncomfortable few months for the Briton who, after his extraordinary feats on the those balmy nights in London three years ago, could apparently do no wrong.
"It's not a nice thing but at the same time, I answered everything that I can and it's not in my control, it's nothing to do with me," Farah told ITV this week.
"At the minute I just want to carry on running, enjoy what I do. I'm very excited to be able to go back in that stadium and compete in front of my home crowd," added the 32-year-old.
Olympic heptathlon champion Jessica Ennis-Hill, another with golden Olympic memories, will be guaranteed a warm welcome as she competes in a variety of events, beginning on Friday with the 100m hurdles where she takes on 2008 Olympic champion Dawn Harper-Nelson.
Kenya's Olympic champion David Rudisha, who broke the world record en route to 800, gold in the Stadium three years ago, lines up over the same distance while Britain's Greg Rutherford, who joined Farah and Ennis-Hill by winning gold on that "super Saturday" will face a tough rival in American Marquis Dendy in the long jump.