In the spring, Lord W travels to London with York, leaving Beauty and Ginger at home. Lady Harriet, who's still at the hall, is an invalid and never goes out, but Lady Anne likes riding horses, and chooses Beauty as her preferred ride. She re-names him "Black Auster," and before you think that's a weird choice, you should know that "Auster" means "south wind."
Beauty enjoys it when Lady Anne takes him out, sometimes with Ginger and sometimes with another mare named Lizzie. Ginger tells Beauty that Lizzie is "rather nervous" (24.2), and a man named Blantyre often takes Lizzie out with Lady Anne. One day Lady Anne insists on riding Lizzie instead because she's more ladylike looking.
Blantyre's really anxious about this, and says that Lizzie is "[…] too nervous for a lady" (24.6), but Lady Anne insists, telling him she's an excellent rider. Somehow we know where this is going, don't we?
They ride to the village to deliver a note to the doctor, and Blantyre dismounts and leaves Beauty to deliver the message. Lady Anne tells him she wants to wait at the gate.
Just then a group of rambunctious horses bolts across the road, led by a boy cracking a whip. One of the horses stumbles into Lizzie, who's so startled that she takes off at a gallop. Beauty gives "a loud, shrill neigh for help" (24.12), and tries again and again but can't get loose from the gate. At last Blantyre reappears, and he and Beauty take off to catch Lady Anne and Lizzie.
Beauty says he "needed no whip, or spur, for I was as eager as my rider" (24.12). Blantyre catches on, and lets Beauty run. They chase her for over a mile, and when the ground becomes uneven, Beauty hopes to catch them. Blantyre's an excellent rider, and he guides Beauty skillfully enough that they start to gain on them. Lizzie tries to jump a dyke and falls, but Beauty makes the jump.
They find Lady Anne motionless on the ground. Blantyre tries to revive her, and calls for help. Some nearby men hear his cries, and Blantyre tells one of them to ride Beauty to get help.
They make it back to Earlshall after going for the doctor, and Ginger is sent out in the carriage to fetch Lord George. When she returns, she tells Beauty what's happened to Lady Anne: Ginger has heard that "[…] no bones were broken, but that she had not spoken yet" (24.28).
Blantyre comes to visit Beauty after the accident and tells Lord George that he's sure Beauty knew what was happening (24.31).
It seems Lady Anne's going to be okay, and Beauty thinks things might be improving in general.