There's no easy way to do it but the Doctor really thinks it will help. He needs to be careful about it though because for all of his cold heartedness, the Master can be surprisingly sensitive at times. And the Doctor is willing to admit to himself that sometimes he isn't the most considerate of aliens.
So, considerate...
"I think we should get a pet." He meant to bring the subject up casually but instead blurted it out.
"A pet? Whatever for? Another human for you to love for a little while and then forget about and neglect?" The Master hasn't looked up from his newspaper but the Doctor can tell he's amused. Better than upset.
"No..." the idea is to work on the Master's issues after all.
"Then what? Pass the sugar." They were having tea at the time.
"Well...I thought that getting a pet might make...you...more..." Bugger, he should have prepared something and written it down beforehand. The Master's switched from amused to annoyed now, not a good sign, the Doctor's going to end up with superglue in his hair gel again.
"Make me more what, Doctor?" he's using that tone of voice, the one that promises superglue hair gel and collapsed galaxies.
"More...happy?" The Master's folded his newspaper and his arms across his chest and is glaring now. And the Doctor doesn't think it's due to grammatical errors.
"Umm...well I thought that you might like to have something other than me to be...companionable with."
The Master's snorts, "and pray tell, just what kind of pet were you thinking of?"
Honestly this was better than he had expected so the Doctor soldiers on.
"Well, something small, easy to take care of and...well...safe." The Doctor gives him one of his winning grins, hoping that that would make things easier to take.
"Something that's not even remotely interesting you mean." The Master's shifting back towards amused now, though the Doctor is still never really sure if it's a good sign or a bad one, even after all this time.
The Doctor runs his hand through his hair, "Now just because they're not dangerous doesn't mean their boring. I mean, puppies! Full of fun! And life and so loyal."
The Master gives him a look that plainly says if you bring me puppies I will torture them. At least the Doctor thinks that's what the look means, he'd better check.
"So if I bring you puppies will you torture them?"
The Master gives the Doctor a very longsuffering look, which reminds the Doctor of the Rani.
"Yes I-
"We should go look for the Rani!" The Doctor interrupts him.
The Master groans and begins to tap out the Drum-beat on the table, something he does less frequently now and generally only when he is really annoyed. A tell that the Doctor had yet to learn to read.
He continues on, unaware of how pissed off the Master is getting.
"-I mean we might be the only Time Lords! Think of it! The old gang all back together!"
At this point the Master decides against clocking the Doctor as he is beginning to worry about his mental health.
"Doctor," he begins, "do you remember the Rani?"
The Doctor looks confused, "of course I do, do you? Is your memory failing? Is it the Drums?!"
"No Doctor my memories just fine," he's grinding his teeth now, "so say we find the Rani, what would happen then?"
"Well-
"I'll tell you what will happen. We find her, she will tell us to piss off. You, of course, won't listen, that will make her mad. I'll end up being kneed in the gonads and she'll probably kill you. Now, does that sound like a good plan?" Which he says very slowly to emphasise how stupid the Doctor's being.
The Doctor actually seems to take a moment to think this over, but the Master can see the moment that the Doctor decides that the Master's completely reasonable arguments are irrelevant. A distraction is needed, so it looks like the Master's getting a pet after all.
"I want a cat!" Just as the Doctor opens his mouth to argue about how being kneed in the bollocks or dead really isn't that bad.
The Doctor gives him one of his genuine beaming grins, the kind that the Master will never admit to liking.
Then he jumps up, shaking the table and spilling most of the tea across the table top and the floor.
"We'll clean it later" and he grabs the Master and pulls him towards the console room. The Master glances over his shoulder. They're going to Earth again, how unexpected.
*****
For once the Master isn't too picky when choosing something. The only thing he's looking for in a cat is that it requires absolutely no care and has a short life span.
The Doctor, of course, wants the perfect cat. Rassilion only knows why.
After a full day of traipsing around animal shelters, pet shops and cat shows the Master has only attempted to strangle the Doctor three times. The Doctor seems to recognise what a monumental effort of will-power this is and decides that they can stop for tea.
The Master decides to annoy the Doctor; he has been awful good so far he deserves a little treat.
"Doctor," he draws out the syllables, making the Doctor look up and blush and get a hopeful look like he thinks he's going to get blown in the cafe bathroom. No chance of that, not after the Master has had to look at 1,264 roughly identical cats. Persians were out of the question apparently because they made the Master look like "a bond villain".
"So, care to explain to me what was wrong with the 1,264 cats we saw today?"
"Well I just didn't see any...good ones that's all. The standard of cats must have deteriorated in the last decade."
"Oh, if only we had a time machine" The Master drawls.
"No, well, we can try a different time tomorrow; we shouldn't give up on this time yet."
"Yes it would be terrible to get me a cat that wouldn't make me more happy, now wouldn't it?"
"Err..."
"Why exactly do we need a perfect cat though?" it's just then that it dawns on the Master why the Doctor thinks they need a perfect cat.
"You're being hopelessly idiotic again aren't you?" The Doctor tries to look innocent but the Master's on to him now.
"You think that if we get the perfect cat it's one step in the direction of the perfect curtains and the perfect house...and...and...You're trying to turn us into one of those couples!" The Doctor looks quite taken aback but that's not surprising because the Master in his fervour had got out of his chair and had yanked the Doctor forward by his tie.
"Umm...one of which couples, Master?" The Doctor's trying to gently pull his tie free from the Master's grip.
The Masters slowly sits down and gives him a sharp look that makes it clear exactly what kind of couple he's talking about.
"Look," says the Doctor raising his hands placating him, well trying to anyway, "between us we're probably the smartest things ever existed, we've died dozens of times, both of us are universally loved and feared depending on where you visit, there has been several religions based on us and we've blown up about a third of the known universe. I really don't think there's ever been a couple like us before and we'll certainly never be boring."
The Master inclines his head a little to concede that the Doctor may have a point.
He blows out a breath and then quirks an eyebrow, "Quite a nice bit of ego stroking there, Doctor," he waggles his eyebrows, "tempted to do some more stroking?"
The Doctor grins and leans forward and kisses him roughly, the Master bites his lip, accepting the Doctor's apology.
"So," says the Master leaning back and straightening his clothes, "can we go get a normal cat then?"
The Doctor nods.
"Good, let's get out of here then."
The Doctor supposes that it's time they left anyway; the couple at the table next to them were beginning to look very nervous.