Unlike the rest of the aliens who came to Earth, Jagar and Hague were not fugitives from SAR TOP. Instead, they were followers of Zin who were sent to Earth beforehand and set up in London, U.K.
Some months after the initial prison break from SAR TOP, Zin sent one of the prisoners - a dangerous Desserian known as Suudor - to London to lure the Tracker (Cole/Daggon) and his human ally Mel there. The plan was to trap Cole in London and capture him, while killing Mel and her friend/former bartender Jess. After getting Cole's attention by committing multiple copycat killings (mimicking killers like John Wayne Gacy and the Boston Strangler), Suudor eventually caught a one-way ticket to London. Cole and Mel - investigating Suudor's actions - managed to learn from information on his computer that he was heading for London and set off in pursuit, unaware that they were been lured into a trap.
When the pair met up with Jess in London, none of them realized they were been watched by Jagar. Communicating telepathically with his brother, Hague told him to follow Cole and the girls but not to get too close - so as to avoid Cole detecting Jagar's presence. Jagar later received some files from Zin, which he in turn gave to Suudor - containing images of both Jess and Mel so Suudor would know his targets to deal with later. Suudor took the files from Jagar but continued his 'work' (as he was impersonating Jack the Ripper), although Jagar saw it as anything but. Needless to say, Jagar did hang around and continued his spying on Cole when he later found the body of Katie - a young prostitute who Suudor murdered that night.
After losing Suudor in the hospital due to having to save a nurse that Suudor threw out of a window, Cole continued to track Suudor. However, he soon felt the presence of Jagar and hid briefly - ambushing Jagar and getting into a brief fight with him. Pinning Jagar against the wall, Cole drew his collector and was able to take Jagar's life force. Learning that Jagar is an Orsian due to the nickel collar around his neck, Cole takes the collar back to the hotel that he and Mel are staying at. Using his computer and a Cirronian device known as 'The Knowledge', Cole attempts to identify Jagar - due to thinking he is a fugitive - but is unable to and instead decides to try to track down Jagar's twin; been anxious that other aliens besides Suudor are in London.
Unbeknown to Cole, Jagar's twin Hague has guessed that Cole has captured Jagar due to him losing contact. To prevent Cole from tracking him down, Hague hides his collar in an abandoned warehouse - preventing Cole from tracking him easily. Cole does eventually track down the location where he thinks Jagar's twin is hiding - but only finds the collar hanging from a chain. Getting in touch with Mel on his findings, he immediately begins traveling to her location after learning that Suudor is after her and Jess. Mel is briefly captured by Suudor but escapes - fleeing into some underground tunnels with Suudor (along with Jess and her boyfriend Ewan) in pursuit.
Suudor catches up with Mel and easily beats Ewan when he tries to save her, injuring him as he hits his head on the stone wall. Thankfully for the trio, Cole arrives and knocks Suudor down - allowing Mel and Jess time to get away with Ewan. As Cole prepares to take Suudor's life force, Hague suddenly appears with a Liquid Nitrogen gun and shoots Cole, weakening him. Suudor then gloats to Cole that the whole thing was a trap to capture him. Despite his wishes to get some 'pay back' for Cole taking so many of the fugitive's life forces, Hague instructs Suudor to finish his task to kill Mel and Jess - with Suudor gloating that he'll bring a 'little souvenir' from both of them.
Alone with Cole, Hague reveals how he took off his collar and hid it in the abandoned factory to ensure Cole couldn't find him easily. He then states that once he and his men have taken Cole to Zin, they will recover all the life forces of the fugitives Cole has captured and find new human hosts for them, including his brother Jagar - gloating that Cole's and Mel's "time on Earth is finished". However, Cole manages to recover enough to enter hyper-time and recover his device before escaping and stopping Suudor from murdering Mel; finally taking his life-force.
Seeing that Cole has escaped from him, Hague and his men (who were already on their way when Cole was initially brought down) begin to search the area from him. By the time they find Cole and Mel, they are too late to stop them from escaping in a taxi. Cole and Mel later leave London, although not before Cole finds out that neither Hague nor Jagar were fugitives from SAR TOP but were sent to Earth by Zin beforehand and had established an organization before the mass escape. However, Cole is still concerned over why Zin tried to capture him in London instead of Chicago.
Later, when Cole has figured out a way to capture all the remaining life forces at once, he found that one 'contaminated' life force was causing issues with the process. After going through several life forces, he eventually identified Jagar's life force as been the cause of the problem - due to having only captured him and not his twin brother Hague, which was causing an energy imbalance. Solving the problem, Cole was able to successfully capture all the remaining life forces in America. According to Cole, Hague and his men in London were also captured as only North America was shown. However, its not revealed if they returned when the life forces began to reappear across the USA.
Tracker (TV Series) - Episode 18: Fever of the Hunt - Part I
Tracker (TV Series) - Episode 19: Fever of the Hunt - Part II
Tracker (TV Series) - Episode 22: Remember When (Stock Footage)