[Tu Mu enumerates the following classes as likely to do good service in
this respect: "Worthy men who have been degraded from office, criminals
who have undergone punishment; also, favourite concubines who are greedy
for gold, men who are aggrieved at being in subordinate positions, or
who have been passed over in the distribution of posts, others who are
anxious that their side should be defeated in order that they may have
a chance of displaying their ability and talents, fickle turncoats who
always want to have a foot in each boat. Officials of these several
kinds," he continues, "should be secretly approached and bound to one’s
interests by means of rich presents. In this way you will be able to
find out the state of affairs in the enemy’s country, ascertain the
plans that are being formed against you, and moreover disturb the
harmony and create a breach between the sovereign and his ministers."
The necessity for extreme caution, however, in dealing with "inward
spies," appears from an historical incident related by Ho Shih: "Lo
Shang, Governor of I-Chou, sent his general Wei Po to attack the rebel
Li Hsiung of Shu in his stronghold at P’i. After each side had
experienced a number of victories and defeats, Li Hsiung had recourse
to the services of a certain P’o-t’ai, a native of Wu-tu. He began to
have him whipped until the blood came, and then sent him off to Lo
Shang, whom he was to delude by offering to cooperate with him from
inside the city, and to give a fire signal at the right moment for
making a general assault. Lo Shang, confiding in these promises, march
out all his best troops, and placed Wei Po and others at their head
with orders to attack at P’o-t’ai’s bidding. Meanwhile, Li Hsiung’s
general, Li Hsiang, had prepared an ambuscade on their line of march;
and P’o-t’ai, having reared long scaling-ladders against the city
walls, now lighted the beacon-fire. Wei Po’s men raced up on seeing the
signal and began climbing the ladders as fast as they could, while
others were drawn up by ropes lowered from above. More than a hundred
of Lo Shang’s soldiers entered the city in this way, every one of whom
was forthwith beheaded. Li Hsiung then charged with all his forces,
both inside and outside the city, and routed the enemy completely."
[This happened in 303 A.D. I do not know where Ho Shih got the story
from. It is not given in the biography of Li Hsiung or that of his
father Li T’e, _Chin Shu_, ch. 120, 121.]