10 Video Games You Didn't Realise Were Secretly Sequels
7. Days Gone - Syphon Filter
On the one hand, you've got a spy thriller full of espionage and counter-terrorism; on the other, you've got a zombie-infested post-apocalyptic horror fronted by a biker. One of these things is not like the other, and yet, Syphon Filter and Days Gone are related. In fact, the latter is a loose sequel to the former.
The journey of Deacon in Days Gone places you in a ravaged Oregon, battling against hordes of the infected, known as Freakers. Where did the virus affecting these people come from? Well, some fascinating Easter Eggs pinpoint a direct connection to Syphon Filter, implying that it is a strand of the titular virus.
There are many general allusions to SF, such as the NERO soldiers resembling CBDC operatives and an unlockable taser with the protagonist, Gabe Logan's, initials on it. However, the most clear-cut evidence comes from documents found in the Cloverdale Laboratory. These documents name-drop the characters Gabe Logan, Lian Xing, Teresa Lipan, and Lawrence Mujari directly, as well as locations targeted by the Syphon Filter virus, and terrorist organizations.
From piecing this evidence together, it is clear that Days Gone is a quiet follow-up to this spy franchise.