This is kinda complicated, so bear with me.

At level 20 I let Preston talk me into taking back the Castle. Things were fine up to that point.

So, Preston and crew were supposed to wait at the meeting point while I went and checked out the situation at the Castle unless I got in trouble, then they were suposed to come running up to help. I got almost close enough to see into the Castle, was still undetected, when Preston et al came charging from behind, with the result that two out of three ordinary minutemen didn't survive the battle past the first thirty seconds or so.

Next, having successfully cleared the Castle, I needed to power up the radio, so I went scrounging for aluminum to build a generator with. Managed to power it up, got my XP for the quest, and had to get out of the game for RL things. Here's where it got weird.

When I restarted the game, I was in the Castle, I checked my quest log and saw that I needed to destroy the egg clutches before they hatch. I had already done that, eh? So I loked around, and had quest markers in all of the spots where the clutches used to be, but there was nothing there. I even tried lobbing grenades on the spots where the markers were, with no results at all.

I shrugs my shoulders I does, but then I realize Preston is following me everywhere I go. When I open his dialogue, I get only the option to make him a follower, talk, and two useless options I don't recall, but neither of them had any effect. When I clicked on talk, he only says we need to concentrate on retaking the castle.

After a while, I decided to lave for another quest nearby, hoping things would get sorted out when I returned. Went to Nordhagen, Preston followed me all the way. turned out i had already cleared the Nordhagen quest, so I then tried to make Preston a follower, thinking I could then dismiss him maybe.

So, Dogmeat was banished to the Castle (couldn't send him to Sanctuary for some reason), and when I went to talk to Preston he gave me the whole quest starter for the castle again. I said I had already cleared the castle, and he said how great that was, and all by myself, too... then he wanted me to meet him and the Minutemen near the Castle. I say okay, but he still won't quit following me and just go to the meeting spot, and when I try to talk to him he just says "We need to concentrate on retaking the Castle!"

So, I just swam straight back from Nordhagen to the Castle, but I was alone when I arrived. I thought Preston would be with the other Minutemen, so I went to meet them. Instead of them, I was greeted by two Raiders and a lot of bullets. They were the only ones waiting there. Well, the two Minutemen who had died in the Castle battle were also there waiting, but they were still dead (I guess they didn't like laying around in the Castle). No sign of Preston.

I go into the Castle, and the mirelurk clutch markers were gone, and the quest log shows the Castle as under Minuteman control. It also says I need to talk to Preston, but there's no sign of Preston. After awhile, I notice there is a quest marker indicating something 70 units or so out in the bay.

I swam out, and no sign of Preston, until I swam to the very bottom where I found him sitting like he was waiting for breakfast or something. He doesn't respond at all to attempts to talk, and he won't leave his new favorite vacation spot under the sea... even though he did stop sitting. Now he's just treading water down there on the bottom.

I have no idea what to do next. Any thoughts?

By way of update, when I reloaded the game this last time, nothing changed immediately, but... I went into the CAstle area and opened the workbench. When I did that, Preston immediately appeared by the transmitter. He gave me the whole speil again about how great it was to have the castle and radio functional, and when he finished, I got the XP for finishing the quest for a second time.

At that point, the markers for the mirelurk egg clutches reappeared, and while the quest as a whole shows a done, that part remains apparently unfinished. On the bright side, Preston apparently forgot he was now supposed to be a companion (though Dogmeat didn't rejoin me), and he's now chilling at the Castle.

I guess while it's a little screwball, the problems are over for now... at least until I talk to Preston again. For now at least, I've turned the speakers off, and am looking forward to "clearing my deck" before getting back to Preston.

A lot of people on this forum would call that a win. You hit the jackpot buddy

Seriously though, reloading a save to before you had to retake the castle would be an option, depending on how willing you are to lose what you have done since then.

If you are on PC, there are console commands to reset and complete quests, and you can disable and enable NPC's and reset them too.

I tend to play it safe in games like this. Bugs don't tend to just sort themselves out if you ignore them so if something doesn't look legit I reload and do the mission again, rather than spend 20 hours doing other stuff and then realising I have borked my save.

That happened to me with a Corsair I was supposed to be meeting. He was chilling out underwater at the bottom and couldn't be interacted with.

If you are on PC, do this:

1) Hit '~' to bring up the console when you are next to Preston underwater.

2) Click on Preston. An ID number should appear in the middle of the console.

3) Hit '~' to close the console. Swim back to shore, and get somewhere that is well onto dry land.

4) Hit '~' to open the console. The ID number should still be displayed in the middle.

5) Type 'player.placeatme'. Hit Enter.

6) Hit '~' to close the console, and Preston should appear in front of you, none the worse for wear.