SPI (Super Protection International) was a fake spy agency and rival organization to WOOHP. In the episode "S.P.I.", SPI agents continually managed to capture various international "criminals" before WOOHP, making that agency appear ineffective while also building up SPI's "good" image.
WOOHP was then shut down and replaced with SPI, but Samantha was very suspicious and investigated SPI further, discovering that the "international criminals" SPI had been capturing were in fact employees of SPI, and that all the criminal incidents had been set up by Geraldine Husk in order to build up positive publicity for SPI and discredit WOOHP.
Upon being captured, Sam later discovered that Geraldine had created SPI as part of her plan to exact revenge against WOOHP for not choosing her as a spy in her younger days.
The girls reunited and managed to defeat their SPI counterparts while exposing Geraldine and the SPI organization as being nothing more than a fake organization. And although SPI soon dissolved and WOOHP reopened again, Geraldine would eventually become a recurring problem for the spies and WOOHP.