Pete Crenshaw is Second Investigator in the firm and serves several roles. First, he is the most muscular of the Three Investigators and is able to take on the more physical demands of the job. Secondly, he has a little more fear of the unknown compared to Jupiter and frequently serves as a source of comic relief (and a reflection of how we readers would feel in the same situation) by his contrast with Jupe's strong-headedness. "Terror Castle" is full of such examples ("If I have to record anything, all you'll hear is the sound of chattering teeth."). Third, he is a frequent companion of Jupiter on stake-outs and other field trips, particularly in the earlier mysteries, when Bob is unavailable.
Despite his apparent fear of danger, Pete frequently acts courageous. For example, at the end of "Stuttering Parrot" when Pete and Jupe are being pursued in the graveyard, Pete sends Jupe to safety while he himself serves a decoy. So despite his tendency to protest dangerous missions, Pete in part overplays his resistance to danger because he also loves a good mystery. The one time when he and Jupe have a genuine argument is in "Whispering Mummy" when Pete is entirely uncomfortable with the implications of a whispering mummy and instead wants to tackle the less fearful case of a missing cat. The two split up for a few chapters but discover that their individual cases are linked, thus bringing Pete and Jupe back together.
While he may not have the intellectual ability of Jupiter, Pete is nonetheless viewed as an equal in the stories and is able to point out Jupiter's own shortcomings (usually in a comical fashion). He is also capable of making deductions and sometimes serves as the clue-bearer instead of Bob (such as in "Talking Skull" when it is Pete who says "under the four," thus reminding Jupe of Spike's speech defect and pointing the way to look under the "floor").