First we start off in 1985, the year where the trilogy begins. Marty and Jennifer take a look at the discolored courthouse. The time is frozen at 10:04, and it's been like that all of their lives. Lightning had struck it 30 years before, and it had never been fixed. Although, the lady who wanted to "Save the Clocktower" was pretty determined to have it stay as it was, "as part of our history and heritage".
Then, Marty is accidently sent back in time to November 5th, 1955, the year the clock was struck by lightning. Coincidently, and luckily, Marty had the flyer that showed when the lightning was going to strike: on November 12th! This was important because Marty had no extra plutonium to get back, so the young Doc created a plan using the lightning, which would generate the 1.21 gigawatts needed for time travel. We see here the tower being struck by lightning.
The morning after Marty returns to 1985, Doc comes back from the future to "do something about your kids!" After going over the plan, Marty checks out the future Hill Valley before going to the Cafe 80's. He sees that a pond was put in, in place of the parking lot that existed in 1985. There are glass windows now, and remarkably, after 60 years, the time is still frozen at 10:04.
Unfortunately for Doc and Marty, Old Biff steals the Sports Almanac that Marty bought in the future and brought it back to his younger self. Because of this, Biff became rich and powerful, and "turned Hill Valley's dilapidated courthouse into a beautiful casino hotel". Destroying a landmark! Marty and Doc had to go back to 1955 to retrieve the almanac. Oddly, Old Biff went back to November 12th, 1955, the 'date of the famous Hill Valley lightning storm'. This posed some problems for Doc and Marty, since they're other selves were there. But Marty finally managed to steal the almanac from Biff, again causing him to crash into a manure truck!
As Marty was burning the almanac, the DeLoreon (with Doc inside) is struck by lightning. The Western Union guy comes with a letter that was waiting to be delivered for 70 years! 'It's from the Doc!' Marty goes back to the younger Doc who faints at the site of Marty being back again. Doc's letter contains the location of the DeLoreon and instructions to fix the time circuit micro-chip with 1955 counterparts. Also there is a warning not to come back to get him, and to go straight to 1985. But just before leaving the mine with the DeLoreon, Copernicus (Young Doc's dog) is whimpering by a grave. Marty sees it's Doc's! Marty decides he has to go back to save Doc. Within a few days the DeLoreon is ready and Marty heads back to 1885 to prevent Doc from being shot by Buford Tannen. Here is a shot of the clocktower being built.
Back to Hill Valley!