First be warned. There is not the least bit of "Doctor Who" in Tennants performance of the sociopath Brendan Block - which only highlights what a great actor he is. When I watched "Secret Smile" for the first time, I had to leave the room on some scenes(I do not watch too many psycho-thrillers, you know ...). The second time, I could really enjoy Brendan Blocks evil genious, how every word, every move, every glance is used with such perfect precision to destroy the life of his ex-girlfriend. It's just creepy.
By the way: Tennant uses his "native tongue", so I needed some weeks afterwards, until I could enjoy listening to a scottish accent again without shivers going down my spine. ;o)