Once again the ubiquitous ''Aliens attempt to conquer the world'' storyline is imposed upon us in the form of the BBC's new drama series Invasion Earth. Aiming to match such commercial successes as imported American cult hits The X Files and The Outer Limits, Peter Haining's companion guide for the purely fanatical strives to provide detailed examinations of various aspects of the programme and related concepts behind its central plot themes. Television tie-in books are notorious for being of a poor quality, often seeming shoddily pieced together, badly written, and very much lacking in substance, being marketed with a sole purpose of money-making. Sadly this publication proves to be no exception.

Haining elaborates on numerous areas of Invasion Earth, describing the processes involved in filming, scripting, casting and directing, and set and costume design. Also incorporated is the scientific and astrological theory inspirational to the drama. Flitting from one subject to the next in a disorganised and almost random manner, with no fluid link between chapters or topics, we swing from the technicalities of V-Rockets as used in the Second World War, to the construction of polyvinyl space-suits and then on again to the alleged sightings of UFOs in Bonnybridge. The legend of ''Nessie'' even merits two pages of irrelevent text plus infamous indistinguishable photographs as a result of reported ''bizarre happenings'' while shooting a scene in the loch.

Other similarly overlong instalments, including drab on-screen and off-screen character profiles, fail dismally to add any interest to the content, while accompanying colour photographs serve only to pad out huge chunks of space instead of complementing written material.

Haining does, however, succeed in including the odd factual gem. On a comprehensive level (somewhat more simplistic than Stephen Hawking's A Brief History Of Time), he attempts to explain such phenomena as blackholes and infinite dimensions, neither patronising the reader, nor using overly complicated terminology. Although rare, these snippets do provide food for thought, with greater emphasis on the extent to which events occurring in Invasion Earth could feasibly happen in the future.

In spite of that redeeming feature, Peter Haining's Invasion Earth Companion continually misses the mark. Easily condensible, it is inconsistent throughout and devoid of sufficient material to satisfy hardened sci-fi junkies. A disappointing representation of what promises to be a popular television series.