B's winning the trick with the queen shows that Z has not got the king.
Trick 7.
Tricks AB, 4
YZ, 3
7. Y B↷ Z A
10♣ 7♣ 5♣ A♣
Remark (Trick 7).—B returns his partner's lead of trumps (see p. [125]).
This is the important trick of the hand. Note the card returned by B, the seven, and if in doubt as to the fall of the trumps, look at the previous trick (see Law 91, p. [18]). In that trick, the small clubs that fall are the three, six, and four, and in the present one, the seven, five, and ten. Nobody having played the two, A may place it by inference in B's hand, for the adversaries not winning the trick may be supposed to play their lowest cards. Assuming B to hold the two, it may be inferred that he has that card and no other left in the suit. For he returns the seven, a higher card than the two; and the rule is to return the higher of two remaining cards, the lowest if holding more than two (see p. [80]. Consider carefully the example given there, and apply it to the present situation).
The king and knave are therefore in the opponents' hands, and divided. Z has the knave (which he turned up), and he has not the king, as he could not win the queen in the previous trick. Y must consequently hold it.
It may be objected that this train of reasoning is too close and elaborate to serve the purpose of inexperienced players. It is, perhaps, a little difficult for an elementary hand; but the careful observance of the rule of play respecting returned leads is so important, that it has been deemed advisable to insist strongly upon it. Of course, when playing with those who do not attend to the conversation of the game, all pains bestowed on working out the position of the cards from such data as the preceding is so much trouble thrown away.