Things are tense for Frank Remnick in The Last Frontier season 1 episode 7, Change of Time. One has a feeling that things are about to blow out of proportion, which will not help matters. While the electricity is restored in Fairbanks, Frank has endless cases to deal with. They still don't know who Thiago is, Havlock is still nowhere to be found, and there are still two remaining inmates on the loose.
While most of those existing mysteries get a conclusion at the end of The Last Frontier season 1 episode 7, Frank also has a breakthrough in the case that started it all, the plane crash in the premiere episode. Frank has a reason to believe that Sidney Scofield, with whom he has developed some sort of partnership and friendship, had orchestrated the plane crash.
He doesn't know why, but he knows Sidney lied to him about certain facts, including Thiago's identity. Meanwhile, Frank's secret has finally come to light, and while his case can be considered a success, his family is breaking apart.
Disclaimer: This article contains major spoilers for The Last Frontier season 1 episode 7. Reader's discretion is advised.
Why does Frank believe Sidney was the reason for the crash in The Last Frontier season 1 episode 7?

There are plenty of big reveals in The Last Frontier season 1 episode 7. Despite the series giving Frank some sort of endgame about the ongoing manhunt on Havlock and the rest of the escaped convicts, there's another discovery that complicates the puzzle even further. While trying to find out Thiago's real identity, they come across several random photos snapped by a local paper 25 years ago.
Everything about the man has been wiped except for those photos. However, Sidney Scofields previous comments about the people in the photo, particularly the little girl in it, "That little girl could be my age now," leads Frank to Thiago's discovery. It turns out that the girl in the picture is Sidney herself, and the man behind her is her father. Next to her father is Vincent Thiago.
The Last Frontier season 1 episode 7 ends with Frank questioning everything he knows about Sidney. He thinks Sidney lied; she knew who Thiago was all along, and according to Frank, she's the one who brought down the plane. It's only a theory at this point, but there are reasons to believe what Frank is saying. If Thiago is working for Sidney's father, then he's essentially working for Sidney.
Also, the malware used to bring down the plane in The Last Frontier season 1 premiere was in his possession, the same malware that Sidney created. However, Frank's discovery may already be too late because Sidney and Havlock have left Fairbanks.
The Last Frontier season 1 episode 7: What is Frank's secret?

Frank's secret, as first revealed in The Last Frontier season 1 episode 3, turns out to be a piece of evidence from Chicago. It's a gun from a case he worked back in the day. He hid the evidence to fix a flaw in the system where he lied so that a certain criminal, who was way too slippery, would be put behind bars once and for all.
Frank and his partner Mike pinned a murder on that man, knowing that the prints on the gun belonged to someone else. But they did it because they thought it was their only chance to put such a dangerous criminal and repeat offender from killing more people. However, the criminal's brother somehow found out and put a hit on Frank. They try to kill him while he gets ice cream with Ruby and Luke.
Luke was still at the store, but Ruby was inside the car and talking to Frank by the window when the hitman takes a shot at him. Ruby dies in Frank's arms that day, and Luke sees his sister take her last breath. The biggest betrayal is that Frank kept Sarah and Luke in the dark about the real reason Ruby died. Sarah and Luke decide to live with an aunt in the end, needing some space after Frank's revelation.
Does Havlock get his hands on the Archive 6 in The Last Frontier season 1 episode 7?

Frank finally catches up to Havlock in The Last Frontier season 1 episode 7, and it's mostly because Havlock has started to become sloppy. Plus, things started to go bad for Havlock early in episode 7, with the CIA, care of Junie, finds a way around the dead man's switch and blocks Havlock from accessing Archive 6. Briggs has also found a way to find Havlock's lair after the blackout is reversed.
That said, Havlock still finds another way to get his hands on the Archive 6 with the help of an airman and a crook named Jamal. He shows Havlock the nearest NSA listening post where he can access the Archive 6 through the system. And while he is able to get whatever sensitive information he wants that can bring down the CIA, Frank is also able to intercept him on the way back to the mainland.
The Last Frontier season 1 episode 7 gives Frank an endgame. Havlock is captured, and he's left Fairbanks with the FBI and Sidney.
Catch The Last Frontier season 1 episode 7, along with the show's previous episodes, only on Apple TV+.