Felicity is really mad with her twin, Sophie, who accidentally left their Magic Book up at the stables and by next morning it's vanished! Felicity holds Sophie firmly to blame, but is she?Finding one remaining torn page and its special pen, it's just strong enough to write a poem to help them in their search. But with very little magical power, the words are all jumbled up and it's more of a riddle than a poem.Three friends arrive for a sleepover, leaving the girls no choice but to enlist their help as it seems The Book is in grave danger! But it's cleaver, and has left a trail of pages and poems for the girls to follow - right through a waterfall, into a concealed land beneath a lake! An amazing discovery, involving their own two ponies and a past acquaintance, means things continue to get even weirder as, together, they enter this murky, unwelcoming world.Majestic, but resentful, Unipegs await them - standing in their way to recovering their Book. With time is running out, tempers begin to fray; it starts to look like The Book isn't going to be the only casualty in, what could turn out to be, Sophie and Felicity's last adventure!