Callan: Season 2, Episodes 14-15 (complete)

Episode 14 Nice People Die At Home - In order to get to an old enemy who failed to kill him once before and got the girl he was with instead, Callan impersonates a Russian agent taking over from a long established father and daughter team who run a pet shop and act as 'spy postbox'. Clever use of all the 'deaddrops' and 'cutouts' that agents use gives a good atmosphere as the cat and mouse game continues throughout the episode between Callan, the father/daughter couple and his target, the Belukov (frustrated by his new desk job and all too capable of potentially turning the tables on Callan - marvellously played by Frederick Jaeger). Callan's feelings about the mission are seen subtly change throughout the episode and there are interesting surprises on both sides of the East/West rivalry in the finalé. A good character episode for Callan and, in fact, a good episode all round.

... and any episode which starts off with a girl polishing a tortoise can't go wrong really :)

Episode 15 Death of a Hunter - But which hunter is going to die; the eponymous Hunter, the code name for Callan's head of department, or could it be one of his two 'human hunters' Callan or Myers... or their enemies. A complex and twisted start in search of a departmental leak sees Callan arrested but it's soon revealed all is not what it seems. The episode keeps up the tension of wondering who you can trust, with potential twists at any time as Callan suffers a drug-induced interrogation, and in the end delivers a great, if by this time maybe slightly predictable, payoff. An excellent rounding off of the series with a smart, implied cliff-hanger almost as an aside.