Doctor Who: The Time Splicer (The Time Splicer Series Book 1)

Book I of the series: The Morning Star
Time has proven to be not so immovable as all have believed.
Time can be undone.
Time can be re-written.
Time can change its mind.
Or at least that is what it appears to do when Martha does not leave the Doctor as she had planned to do.
Having just walked around the world and suffering much emotional, physical and mental post traumatic stress as a result, Martha goes to the Doctor to tell him that she intends to end her travels with him. Yet as she does so, she finds herself confronted by a masked figure that changes her mind. Thus leading her to another adventure with Ten, where time gets warped, reality begins to fold over on itself, and both the Doctor and Martha come across a new threat right in the middle of space.
Here comes an adventure after Series 3, that none knew occurred.