Doctor Who's fourth season continues with a definite upturn in both quality and direction with the next batch of episodes. The two part `The Sontaran Stratagem' and `The Poison Sky' sees the return of those classic Who villains to plague our Timelord once again. Martha calls The Doctor back to Earth when a UNIT operation to infiltrate and shut down ATMOS satellite navigation systems goes ahead. The simultaneous crashing of cars around the world, all using ATMOS, and a series of unexplained events lead UNIT to believe that there is an extraterrestrial presence behind the system. The story is not too bad but there are several problems with the execution. While it's nice to see the Sontarans again, they don't seem to do much, plotting and scheming in the shadows rather than just fighting it out. The battle between the Sontarans and UNIT forces was quite good but too short and it never gave you the feeling that the Sontarans were a great military power. The final sequence has been lifted right out of `Voyage To The Bottom Of The Sea' or for those that remember it, `The Centurions' episode `The Sky Is On Fire' and as such it feels like a cheap end to what could've been a great dramatic moment. The writers also seem to have turned Martha from the strong character we saw develop throughout season three to a more ineffectual, two dimensional and screaming emotional sidekick which is a real shame. Great to see Bernard Cribbins back again though and his moments with both Donna and The Doctor are excellent. `The Doctor's Daughter' is a nice and well plotted self contained episode. The TARDIS deposits The Doctor, Martha and Donna on the war torn planet of Messaline. They are captured by soldiers and a tissue sample is taken from the Doctor in order to generate a clone soldier, his `daughter'. When Martha is captured by the amphibious Hath, The Doctor tries to unravel the cause of the war, while dealing with the sudden shock of becoming a `father' again. The story is well written and gives an insight into The Doctor who has previously only mentioned his family in passing. His reaction to Genny (played by 5th Doctor Peter Davison's daughter!) is excellent and the interplay between him, Genny and Donna is hilarious. The Hath are one of the best alien creations of the series to date and the relationship that develops between Martha and Peck is touching. The end of the story is rather predictable but still entertaining and no doubt the ramifications of this will return at a later date. `The Unicorn And The Wasp' is quite possibly the best episode of the current season to date. The Doctor and Donna arrive in 1920's England at a garden party where one of the guests is none other than Agatha Christie! When a murder occurs in the house, the Doctor, Donna and Agatha find themselves trying to uncover who the killer is before more people meet an untimely end. This is classic Who stuff and has been written by someone with an obvious passion for Christie novels (see how many titles you can spot!) and a great murder mystery. The pre-titles sequence is a hilarious parody of Cluedo and the story satisfies on all levels. The CGI is up to its usual standard and used to good effect and the whole episode feels like they've finally figured out the formula this year for a damn good Who adventure. Let's have more of the same please! This season has started to settle down after the tenuous beginning but the writer's still need to tone down the `angry Donna' bit and to stop making jokes about them being taken for a couple, it's beginning to wear thin now as they do it nearly every show. This collection of episodes stands head and shoulders above the first disc and lets hope that this trend continues to the huge end of season finale that we all know is just on the horizon.