Plan B - Reuven's:
Second Degree Murder
As you read Reuven's plan, be sure to differentiate between what Reuven says (to his brothers) and what Reuven thinks (to himself):
"And Reuven said ... 'Do not shed blood, cast him into a pit [in order that he die] out in the midbar (wilderness), but do not touch him yourselves.'Reuven's 'official' plan is to let Yosef die a less violent death, i.e. to throw him alive into a deep pit instead of murdering him in cold blood. However, his 'secret' plan is to later return to that pit and free him.
[End of quote! Then the narrative continues by informing us of Reuven's true intentions...]
in order to save him [Yosef] from them and return him to his father." (37:22)
Note how Reuven even suggests the specific 'pit' in which to throw Yosef - "ha'bor ha'zeh asher ba'Midbar!" Most probably, this is so that he can later sneak away to that pit and save him.
[Compare this to the brothers' original plan to throw him into "one of the pits" (37:20) - possibly a pit closer by.]
Unaware of Reuven's true intentions, the brothers agree.
Yosef arrives, and in accordance with Plan B, the brothers immediately strip Yosef of his special cloak and throw him alive into the pit (see 37:23-24). Afterward, they sit down to eat (see 37:25). [A "seudat mitzvah" most probably - "v'akmal!"]