The nine-year-old has enjoyed something of a renaissance this season after being restricted by injury.
Third in the Queen Mother Champion Chase in 2009, Petit Robin has switched with great effect back to hurdles with solid wins at Ascot and Sandown this term.
Henderson's raid on this valuable prize is backed up by Cash and Go, Lyvius and First In The Queue.
Alan King has the strongly-fancied Balder Succes while Tom George has declared Racing Post Hurdle victor Olofi.
The lightly-raced Ranjaan represents the Paul Nicholls stable while David Pipe has two likely outsiders in Kazlian and Dan Breen.
Jonjo O'Neill's It's A Gimme and the Brian Ellison-trained Bothy feature in a fascinating list.
There is also a strong challenge from Ireland in the shape of Gordon Elliott's Cause Of Causes, Willie Mullins' Rattan, Eddie Harty's Princeton Plains and Thomas Edison from Tony Martin's stable.
The going at Ascot is currently heavy, soft in places, but with further rain forecast, clerk of the course Chris Stickels believes it could be simply heavy before today's meeting.
"We've had 28 millimetres of rain since late yesterday and the going is heavy, soft in places," said Stickels.
"At the moment we are OK and coping with what we've got. At the moment we are quite happy and will monitor it as the day goes on. Potentially we could get seven up to nine millimetres.
"If we do get that we may have to call a precautionary inspection, but at the moment it's taking it.
"The forecast is for the rain to die away tonight and for it to be dry for 24 hours.
"Wet weather is coming in tonight and the early hours of Saturday when the next rain band is due."