Lareen was a Thal spy sent to board the Dalek shuttle that had picked up Davros from the planet Necros and was taking him to Skaro for trial. She used stealth technology to evade being detected, and was given two options to deal with Davros: either she could be his assassin or his enlightenment and freedom. Using her stealth suit, she evaded Dalek sensors and infiltrated Davros' prison cell, eventually revealing herself to him. The two engaged in a debate, in which Lareen attempted to turn Davros against the Daleks, telling him they would never accept his claim of authority over them due to his mental instability and arrogance.
After the Dalek shuttle landed on Skaro, she gave Davros a smuggled capsule of Movellan virus and asked him to release it on the planet's population during his trial. Instead, he exposed her to the Daleks — an act which won him favour amongst the Daleks. Lareen managed to evade the Daleks long enough to send a final report back to her Thal superiors. She was then captured and brought to Davros — now the new Emperor of the Daleks.
Despite having failed her mission to kill or convert Davros, Lareen remained defiant, insisting the Daleks would never truly accept Davros as their leader. She also claimed that Davros must know his creations were evil, pointing out that he actually considered releasing the virus on Skaro — something he admits to. Davros then ordered his Daleks to exterminate her, which they did. (AUDIO: The Davros Mission)