Dr Owen Harper knows what humans are. He knows every bone in their body, every muscle, every tendon, every bit of sinew that holds them together. It's a part of his job you see. As a doctor, you would presume so anyway. You'd assume that a doctor would know what they were talking about, would be able to empathise with what you were feeling – because that's what humans do after all – they emote. They feel. That is what, fundamentally, makes you different to other people.

So yeah, Owen figured that he knew people. He knows what makes them tick, and he can read them like the proverbial book.

There are times however, when Owen doesn't want to feel, but feels too much. He feels everything at once, and every single bad memory comes back to him. His Mother – of course, she said she loved him, but then again, she didn't like him. He never knew the love of a parent growing up, so struggled to love unashamedly himself; until Katie came along.

Katie was like a sun, a thunderstorm, fire, ice and blessed heat. Owen loved her much more than he should have done, he allowed himself to be too in love. He didn't know how that felt before, didn't know that it hurt, but sweet Gods it hurt. So he added it to another life lesson, created a new mask.

So many people loved and lost. So many opportunities never taken. So many failures. So many successes. All of them on just ordinary days. 365 days in a year (normally). Most days are the same, you set yourself a routine, and you do the same thing every single day. But then again, Owen thinks, some days are different.

There are days when he'll look out of his window, and all he will see is the darkness; pressing in, all consuming and never ending. There are days when all he wants to do is sleep for hours on end, at least until he sees that tiny bit of light that made it all seem okay. Then he has the days where everything is good. Not necessarily happy days, just the ones where nothing goes badly, it's just right.

This, Owen figures, gives him the right to hide behind a mask when it suits him. On those days where he has to sit and watch as a family's lives get torn apart, shredded to pieces, and maybe, just maybe with time sewn haphazardly back together again, Owen puts on one of his masks – professionalism and sympathy. That mask isn't his favourite. It still shows that he feels, still cares.

His other mask is a blank one. It's the mask that allows him to change and adapt to whatever the situation requires. It is a flexible mask, and Owen rarely uses it. He prefers his final one.

The final mask of Owen Harper is sarcasm. Sarcasm, dark humour, cynicism, whatever you call it, it all amounts to the same thing. Hiding your true feelings with snark. And Owen is a master at this, because after all, in Owen's mind, sarcasm is just a substitute for the tears.