Theodore Too and the Mystery Guest is a book written by Michelle Mulder and illustrated by Yolanda Poplawska. It is the fourth and last of the Theodore Too series.
Theodore Too and Lucy Tug meet a brand new friend, Bluenose II, and learn why everyone loves her. The tugboats, always ready for adventure, hear that Halifax Harbour will soon have a famous visitor - who could it be? With the help of their friends Dartmouth Ferry, George Lighthouse, Fisherman Murphy, and Guy Seagull, they set out to find and welcome the mystery guest. When they meet the beautiful Bluenose II, they make a brand new friend and learn just why everyone loves her.