Arrival of Ruth

[lottanyman]

I'm also currently re-watching series 2 and I'm always looking out for moments between Ruth and Harry but I'm with PF here and would deny that Harry had an interest in Ruth right from the beginning.

If there is anything at all on his side it's more of an irritation on Ruth's enthusiasm which is in total contrast to the usual behaviour of Danny, Zoe or especially Tom who are all ambitious about their jobs but who have long settled in and kind of adapted to the downsides and doubts of being a spy.
Especially in the first episodes Ruth is clearly not yet used to this and is happily welcoming any threat whereas everybody else is just trying to avoid the worst.

In 2.5, in the EERIE episode for example Ruth gets a very annoyed look from Harry when she exclaims something like "Oh goody" while Harry tries to make his team take this excercise seriously and I think he's also a little unnerved when she starts crying upon her explanation of the VX gas so that Harry advises Sam to take over from her.
I think Harry's irritation is slowly going down over series 2 but there is nothing else and him slowly developing feelings for her is only starting in series 3 and even more in series 4.