The Doctor had been travelling through time and space, he was always there to check if anything needed fixing, he had put a lot of work into keeping the universe safe and wanted It to stay that way, it had been a long time since he had to deal with the Master, He didn’t really know what had happened after their last battle. He guessed the Master would no longer be a problem. The TARDIS though was picking up strange disturbances in time. The Doctor started up his TARDIS, he had a jammy dodger in his mouth.

Arriving in 3596 ,Trelloponicis the Doctor stepped clumsily out of the TARDIS and grinned a bit, he was quite excited wanted to look around, but he knew that he couldn’t get too carried around and needed to find who was behind the disturbances in time. He though turned around to see a man . “Master.” 
Ah of course, that did seem like something the Master would do. He just didn’t understand how the Master was here. He knew that the Master wouldn't be pleased that he was here, interfering with his plans. The Doctor though couldn't let the Master get away with ruining time. Even if the Doctor was childish there was moments he was serious when needed to.