Sooo basically the doctor ended up telling Cain that Sid no longer had the compass. From my understanding the compass if a very important weapon/tool that Cain entrusted to Sid. If Sid have it away, it makes their relationship as “partners” questionable. Cain asks to further explain the situation but he instead attacks the doctor and so Cain basically understands that Sid is working against him hence why he attacks him.
Basically sid betrayed Cain.
Ooh I see now I get it tyyy!
Im confused~~~(ﾉﾟ0ﾟ)ﾉ