en_tn_lite_do_not_use/act/25/03.md

to summon him to Jerusalem

Some versions translate this as "to have him summoned to Jerusalem." The word "him" refers to Paul. The Jews wanted Festus to have his soldiers take Paul to Jerusalem.

for they were preparing an ambush to kill him along the way

They were going to hide along the road and kill Paul as he was passing by, but Festus was not aware of this part of their plan.