Dead Rising/Overtime Mode

Overtime Mode is significantly more difficult than 72 Hour Mode because of the Special Forces troops around, and the much tighter time restriction on your activities. The Real Mega Blaster (awarded for getting the Zombie Genocider achievement) and making it all the way to level 50 as well may help.

Overtime Mode
You've got 24 hours to get everything she needs for the serum before Frank becomes a zombie.

Method to Prevent Infection
There are eight items that she needs you to gather, but the order they appear in your mission select list isn't the most efficient. The route below requires you to have rescued Greg on the first day and have picked up the maintenance tunnel key at some point; the shortcuts offered by these optional items make crossing the mall much easier - especially since the Special Forces are back again, and this time they have a fancy new toy.

Leave the hideout and head up to the main area of North Plaza to get a glimpse of it: a small helicopter with a mean gun and a loud alarm. If one catches site of you, it'll call in a lot of backup from the Special Forces, as well as taking its own pot-shots at you. Luckily, their rotors are fairly noisy, so you can hear them before they spot Frank. They tend to move pretty slowly as well, so if you've got a sniper rifle then they're pretty easy to take out - and you'll get a 500PP bonus for each one.

Isabela's List
The things Isabela has asked for, as listed in the game, are: She's also asked for an unspecified number of Zombie Queens, but you've got enough to worry about with this lot for now.
 * Cold Spray - SporTrance, Paradise Plaza
 * First Aid Kit - Seon's Food and Stuff, North Plaza
 * Blender - Food Court, or Columbian Roastmasters, Paradise Plaza
 * Coffee Filters - Security Room
 * Magnifying Glass - Wonder Jewels, Wonderland Plaza
 * Camp Stove - Sports High, Entrance Plaza
 * Developing Solution - Cam's Camera, Paradise Plaza
 * Perfume Bottle - Estelle's Fine-lady Cosmetics, Entrance Plaza

The first item on the list to get is the First Aid Kit, which you'll find the Pharmacy in Seon's. It's on the shelves next to where the medicine was in Medicine Run. The supermarket is crawling with Special Forces though, so be careful. You should also take the opportunity to stock up on health items; wine, located next to the pharmacy counter, is the best option.

Once you've picked up the First Aid Kit, don't go back into Seon's; instead, take the stairs down to the maintenance tunnels and hop into the van down there. From here, drive down to the Entrance Plaza - you'll come out between Children's Castle and Everyone Luvs Books. Head over to the other side and down to the left to find Sports High; the Camp Stove is on a set of stand-alone shelving units near the door.

Head back out into the Entrance Plaza and up the stairs nearest you, then follow the upper walkway along to the north end of the Entrance Plaza. Use the stores for cover, and keep an ear out for the mini-choppers; there's usually one floating around each end of the Plaza. At the top end, you'll find the Perfume Bottle in Estelle's Fine-lady Cosmetics, on the rear corner of the central pillar.

Stay on the top level of the Entrance Plaza and go back down the opposite side than the one you came up on, and then head through the side door to the Security Room, which will now let you through. If you've got the Real Mega Blaster or the Real Energy Sword, you should drop them just before leaving the Entrance Plaza so you can pick up fresh weapons in the Security Room.

The Coffee Filters are on the desk in front of the security monitors - and while you're here it's a good time to save, since you're halfway through Isabela's list.

Take the airvents out onto the Rooftop and then head into the Warehouse. Taking the door onto the shelves is a little easier since the Special Forces on the ground won't be able to shoot up at you, but there are a couple of them on the shelves themselves that you'll have to contend with. Go out into Paradise Plaza and into Cam's Camera right beside the Warehouse door, where you'll pick up the Developing Solution behind the counter.

Head upstairs and pick up the Cold Spray just inside the door of SporTrance, then go across the corridor and into Colombian Roastmasters for health and the Blender Isabela's asked for.

The final item on the list is in Wonderland Plaza, so head down the stairs between SporTrance and Lady About Town and into the ladies' bathrooms to take the shortcut across, and another opportunity to save.

Wonder Gems is directly across from the bathrooms in Wonderland Plaza, and the Magnifying Glass is on a counter near the back of the store.

With everything now in your possession, head into North Plaza and back to Carlito's Hideout - you can use Isabela's motorcycle, parked outside Seon's, if you need to hurry.

Back at the hideout, speak to Isabela to hand over the goodies.

Generator and Queens
When the cutscene ends, speak to Isabela again. This time, the generator's stopped working, and she'll need a replacement. Carlito used the clock tower in the Leisure Park as storage, so there might be a replacement in that area.

Back in North Plaza, head towards Crislips and out into the Leisure Park to see that the zombies have started to make their return. You've also got the Special Forces attack helicopter buzzing overhead, but so long as you keep moving, it shouldn't be too much trouble. It's worth keeping an eye on the zombies though - you'll want to collect any Queens you spot.

Approach the wreckage of Ed's helicopter by the clock tower, and Frank will discover that it's actually hollow, and there appears to be a tunnel underneath it, that could lead outside. The problem is, it's full of zombies - which will provide a major problem to the escape plan.

Examine the maintenance panel on the opposite side of the tower from the zombie hole to find a replacement generator, and go back to Carlito's Hideout to hand it over.

Hand over any you're carrying - you'll have to equip them in your inventory to do so - then head back into the mall to pick up some more. While you're here, it's a good idea to save before venturing out again.

The zombies have made it inside again, but there's not many of them and Queens can be difficult to find. You've also got to watch out for the Special Forces and their mini-choppers. It's not advisable to try to collect all the Queens you need in one go - for a start, you're better to leave North Plaza to let them respawn, and secondly you should keep as much of your inventory for food items and weapons as you can. Finally, you've got to hand the Queens over one at a time, and it's irritating having to do ten in a row.

Escape
When you start this section, you'll be standing on a save point - take advantage of it.

You'll need to keep Isabela close for this bit - she's the one holding the pheromone, so if you get to far apart then Frank will be set upon by zombies. Take her hand and go down the corridor slowly - move too fast and you run the risk of Isabela getting caught on a zombie and losing her grip on your hand.

When you come to the first big gate, open the grate on the left-hand side and let Isabela go through. You'll have to fight off zombies for a few seconds while she's throwing the lever; the double lariat move is the most effective for keeping the zombies at bay until you can rejoin Isabela and take her hand again.

Further down the tunnel you'll come to another big gate, but this one has a smaller door built into it which will let you both through without having to split up.

You'll eventually reach a third gate, which you'll again have to open by letting Isabella through a smaller grate to the side. Again, the double lariat is your friend while you wait; once the gate's opened take Isabela's hand and go down the slope.

Things have been going a little too smoothly so far, though - Frank spots guards here too. The zombies might prove to be an advantage, though - if the main gate ahead is opened, the Special Forces should be distracted enough to let Frank and Isabela slip through.

To get the lever to open the gate, go down the path to the left of the gate and double back up the stairs. You'll have to set Isabela down to throw the lever, so make sure to pick her up again before you head back down the stairs. There's a small side gate here that you can go through, but watch out for the soldiers - you can still get hit by their fire, even if they don't spot you.

Make it to the jeep and get in, and you'll be one step closer to freedom - but Frank's not going to escape without a fight.

What Was Solved?
You'll also have unlocked Infinity Mode.