Does しとこう mean what I think it means in casual speech?

Question

Dear fellow lovers of Japanese language,

I've come across this dialogue in a visual novel:

…って、もうじき七時か。秘密の話はこのヘンにしとこう。いつ人がやってくるか判らないし、朝になったら学生らしく振舞わないとな

The implied meaning is unambiguous here, as it is that they should stop talking secrets and act more like students.

However, I'm at my wit's end with the grammar in the second sentence. Is しとこう a volitional form of しとく (a shortened ～しておく)? That is, does 秘密の話はこのヘンにしとこう。 carry the meaning that they should put these stories down [in preparation] for what happens in the next sentence? It would make sense to me this way but I'm very inexperienced with Japanese language so please correct me if I'm wrong.

Thank you for your patience.

Answer 1

「おく」, when used as a subsidiary verb, can basically serve two functions.

1) Expresses "performing Action A in advance (so it will help one perform Action B in the future)".

2) Expresses "leave something as-is" or "let a situation continue".

Judging from the context given, I would say that we have a case of function #1 in use here.

You have been doing some secret talk (all night) and you want to stop now because it is almost 7 o'clock and people may start coming in any minute. It is time you acted like normal students again.

Action A: Bring the secret talk to an end.

Action B: Act and look like normal students.

Answer 2

しておく means you do something and leave the situation as it is for a while. (I know it's often translated to "in preparation" but that's not accurate in the first place.)

In this case, 秘密の話はこのヘンにしとこう, compared with simple …しよう, sounds a less forcible suggestion, I mean, it's lighter to suggest the ending point around there than to suggest to shut it down.