The Origin of the Species series of supplements is all about providing options for including non-human races - be they characters or NPCs - in your Spycraft game... but this one takes it to an extreme, providing all that you need to play a 'transmech' or in other words a transformer, a self-aware autonomous robot that is capable of switching form between two appearances, based on those common to the world in which they live. Product of some alien engineering - or even 'extreme science' on Earth - you might think they'd be better suited as invading opponents to your band of spies... but it could be quite entertaining to play one instead.
A transmech is a fully-conscious robotic lifeform, not someone piloting a strange mechanical exoskelton ('mecha'), and its important to remember that especially if you are playing one rather than fighting them. They tend to be large and quite obvious, at least in one of their forms. Naturally, they do not work quite the same as people: they do not eat or breathe and do not heal damage in the same way as a human being does. One form is the classic 'robot' style upright bipedal thing, the 'alt-mode' shape it can shift into (quickly, it's merely a full round action) can be just about anything provided it is at least approximately half the mass of the bipedal form (where the rest goes, nobody knows!). Things like vehicles, objects or even animals are allowed. Objects can include weapons, of course. A vehicle can be 'driven' by someone else, just like any other vehicle, and objects can be used as ordinary objects of that type, which could give rise to some interesting situations.
There are a lot of specialties and feats to enable you to customise a transmech to meet your needs, and copious advice on actually building and playing one. There's also a master class to aspire towards, the Legendary Transmech.
Next comes a good collection of campaign ideas - if there are going to be transmechs in your campaign, you will need to work out what they are doing there! As well as these one-paragraph ideas there is a full-blown campaign seed complete with a new organisation whose purpose is to protect at least some of humanity from encroaching transmechs. To get you started there is a horde of developed transmech NPCs, which provide good examples of what you can do with the basic rules herein.
Finally, there are three ready-to-play scenes involving transmechs. They begin with the party as human operatives in a world that has no knowledge of transmechs... but that doesn't last for long! The second one pits the characters as transmechs arriving on a new world and the final one involves said transmech team finding an ancient artefact and having to deal with it as well as the inhabitants of the world they are on.
It's an interesting concept which could prove the basis of a dramatic campaign if it's the sort of thing that appeals. An intriguing thought would be if a party of human agents find a single transmech who becomes part of their team, but you would need some strong role-players to pull that off successfully.