When the first group of characters started to leave the show I was hugely disappointed to see them go, particularly Tom (played by the absolutely brilliant Matthew MacFadyen). If the cast is completely disposable it is far more difficult to convince the audience to truly get involved in their lives, and consequently the viewer is not as invested in the character’s surviving through the episode (after all, the producers will simply right in a new one next week). This is felt even more so for a show coming across the ocean from England, where viewers will only be treated to at most a dozen episodes before it disappears for at least a year and often longer than that (cable networks in this country also tend to produce shows in this manner). This difficulty is far more simple to overcome in a comedy, such as Coupling, where Jeff Murdock (Richard Coyle) left after the third season to be replaced by Oliver Morris (Richard Mylan) in the fourth. As Coupling is far more light-hearted, the viewer (at least this one) needs to invest less emotionally in order to be satisfied.
Even so, Adam Carter (Rupert Penry-Jones) is a worthy successor to Tom and after only one episode the new season seems to firing on all cylinders: there is a mole in the service (something of an old storyline for a show like this one), there is an operative being held at gun point, Harry Pearce (head of the department) has a secret, and the episode will be continued next week.
Despite any weakness in developing the newer cast members, MI-5 is well worth checking out for any fan of the genre.