When siblings Abisai and Charlotte Taylor are gifted an odd bookmark by an anonymous donor, they are threatened and then pursued by an enormous, fearsome stranger. When it is revealed that the bookmark is in fact a BookMarck, and able to transport Abisai and Charlotte into any book at will, they are pulled into an adventure like no other. As they are chased across the storylines of The Three Musketeers, Sherlock Holmes, and The Time Machine, can they reunite across narratives? Can they escape the mysterious Aginbyte of Inwit? And will they ever be able to return home?