Martin has built a dimensional separator, a machine that turns 3D items into 2D. These 2D items will allow Martin to carry more Earth artifacts back to Mars. Will Mrs. Brown be one of those artifacts? She can be as she inadvertently walks in front of the machine and gets turned into a 2D object. As something organic, the 2D Mrs. Brown will remain permanently so in 18 hours. Martin needs a certain metallic compound to restore her third dimension. While Martin retrieves the compound, he turns Mrs. Brown into a painting to retain her flat shape, i.e. so that she won't break. Det. Brennan comes by and sees the painting. As a surprise for Mrs. Brown, the detective suggests hanging it in a friend's art gallery. Tim is helpless to stop him. Later, while Martin and Tim retrieve the painting "after hours", they run into a band of art thieves/smugglers who steal the painting of Mrs. Brown. The smugglers whitewash over the canvasses before they smuggle the pieces to Europe. Despite Martin and Tim being incapacitated during the robbery, they find the thieves' hide-out in a carnival back-room. Now Martin and Tim need to find the covered over painting of Mrs. Brown, and elude the thieves and Det. Brennan, the latter who thinks Tim is the mastermind behind the art theft.
—Huggo