Irish challenger Magic Of Light is out to claim a third successive victory in the Matchbook Betting Podcast Mares' Hurdle at Ascot.
The 2019 Grand National runner-up has landed Saturday's Grade Two prize in each of the past two seasons, having previously won a Listed chase at Newbury a month earlier.
The 10-year-old returns to Berkshire, having recently completed her hat-trick at Newbury, and Harrington is hopeful she can follow suit when facing four rivals this weekend.
"She's gone exactly the same route as the last two years – she's gone to Newbury for the chase and then on to Ascot for this hurdle," the trainer told Sky Sports Racing.
"She's in terrific form, and we've got Jonjo O'Neill junior to ride her. She jumped a hurdle this morning – we thought we better remind her it's hurdles and not fences!
"She's just been amazing. Probably my only worry is the ground is very heavy. Hopefully it won't be too bad."
Magic Of Light's task appears far from straightforward, with Dan Skelton's Roksana a formidable rival.
The nine-year-old made a flying start to the current campaign at Wetherby in October, before finishing on the heels of Paisley Park and Thyme Hill in the Long Walk Hurdle at Ascot last month.
Coded Message (Ben Case), Eglantine Du Seuil (Paul Nicholls) and Midnight Tune (Anthony Honeyball) are the other hopefuls.
The Nicky Henderson-trained Janika heads a field of 12 declared for the Grade Three Matchbook Better Way To Bet Holloway's Handicap Hurdle.
The Seven Barrows handler is also represented by Craigneiche – while Harry Fry's Lightly Squeeze, Tom Lacey's Kateson and course-and-distance winner Danny Kirwan, from the Nicholls yard, also feature.