When Isabel takes a fall while out on a ride, she blames River for her injury. Feeling angry and let down, Isabel refuses to fetch River and go to the Masquerade Ball. The trouble is, while she watches her friends having fun without her, someone else is watching the bond between Isabel and River weaken. Danny will stop at nothing to become a Unicorn Rider. Will Isabel realise her mistake in time to save River and repair their broken bond?