Theory:Timeline - Abby & Zara as they only appear in one story each without the other. The title currently appears as this due to the retitle tag above.
Talk about it here.
This page lists appearances of the Tracers, Abby and Zara, in the order in which they experienced them. This timeline is based upon observations of the Doctor Who universe and the events that occur during each of these stories. From these observations we have attempted to build a concise timeline. It is assumed, much like its TV story counterparts that for each novel or audio series their published/numbered order is the order they occur in. This does not apply to short stories which are often ambiguous about their placement. There are also many gaps between stories.