'When a thief steals two splendid lobsters - kings of the sea - and leaves a secret message on the empty tank, Mr Petrusca is more upset than anyone can understand. Hazel Green knows there's something fishy going on, but it takes all her ingenuity, plus a little help from the Yak, to crack the code and solve the mystery. And even then, Hazel still has important work to do...'
Source: Publisher's blurb.