1997 MIT Mystery Hunt Puzzle 20 Solution

These are clearly chess moves, but if you try to follow them from the beginning, not only do you need to have pieces already in some unknown starting position, but you end up with white capturing his own rook with his knight in the move that wraps around to the second row.

Instead, set up the board in the starting configuration and start at the point part way into the 8th line of moves with d4 d5, which looks like the start of a real game.

1.d4d5
2.Na3Nc6
3.c3Nf6
4.Nb5g6
5.Bh6e6
6.b3a6
7.Nd6Bxd6
8.a4b6
9.Rc1a5

Good so far. Some of the moves are bad chess, but they are legal moves, except for the Bd6 capture of a knight that was only indicated as a normal move. (All the captures for the entire game are treated this way, and check is not marked either, though the en passant capture is marked.)

But the next move is white Ng4, an impossible move since the the only knight he has left is on g1. The moves which follow work if this move is simply skipped.

10.b4axb4
11.Rb1Rg8
12.e3Rxa4
13.Qd3b3
14.Be2g5
15.Nf3g4
16.Bg5Rxd4
17.Qb5Bb4
18.Qa4Ba5
19.Qb5Rd3
20.Qxd5Qd6
21.Qb5Bd7
22.Qa4Bxc3
23.Kf1Bc8

After 24. Qa8, the next move Bd1 does not work. But again it can simply be skipped.
24.Qa8e5
25.Nxe5b5
26.Rxb3Ke7
27.Rb4Be6
28.Nc4Qd4
29.Nd6Bd5
30.f3Nxb4

After 30. ... Ne4, both Nb4 and Qd5 are impossible. If Ne4 is skipped, the next few moves are possible.

31.Qxd5Rd8
32.Qc6Kf8
33.Bd1Nfd5

Qb3 is impossible.

34.Ne4Qe5
35.h4gh3(ep)
36.g3Nf6
37.Bh6Ke7
38.Bb3Rg8
39.Be6Rg6
40.Nd6Kd8
41.Qe4c6
42.Bb3Nfd5
43.Qc4f6
44.Ne8Qe6
45.Rxh3bxc4
46.Nd6Nb6
47.Ke2N4d5
48.Bf8Kc7
49.Rxh7+Qd7

Qe3 was not possible for black's 49th move only because of the check.

50.Nb5+Kb7
51.Bxc4Nb4
52.Bc5N6d5
53.Bd4Rg8
54.Bxf6Qxh7
55.Bb3Ra8
56.Bd4Qh2+
57.Kf1Ra1+
58.Bd1Raxd1++

And this brings us back to where we started. So yes, it is a legal, though highly improbable chess game after these five moves are removed: Ng4 Bd1 Ne4 Qb3 Qe3. The final position is:

-- -- -- -- -- -- -- --
-- BK -- -- -- -- -- --
-- -- BP -- -- -- -- --
-- WN -- BN -- -- -- --
-- BN -- WB -- -- -- --
-- -- BB BR WP WP WP --
-- -- -- -- -- -- -- BQ
-- -- -- BR -- WK -- --

Here is the set of moves, with the starting point and the 5 skipped moves marked.