On the whole, the BBC audio series by Paul Magrs with Tom Baker reprising his Fourth Doctor have not really grabbed me. But I felt that The Hexford Invasion, the fourth of the Serpent Crest series, was a significant improvement, largely because the excellent Susan Jameson is given her head as the Doctor's housekeeper / companion Mrs Wibbsey. She was rather callously left behind to do the dishes at the end of the last episode; now she must suddenly deal with Mike Yates and UNIT, showing up with a scruffy but authoritative little man who calls himself the Doctor but is nothing like "her" Doctor. Magrs, and even more so Jameson, superbly capture the fannish feeling of confuion and loss when the Doctor one knew best is replaced by someone else (especially if your favourite Doctor is Tom Baker) and though the plot is as absurd as usual the three main cast are all brilliant. David Troughton doesn't sound hugely like his father (I thought he was more Pat-ish in Titus Andronicus), but we are left in some doubt as to whether his character really is the Second Doctor, and anyway he is up to his usual standards. And the Tom Baker / Susan Jameson chemistry has never been better. I hope that the final episode in this sequence matches this. ( )